It may seem silly, but a good way to get Mandarin phonetics down is to watch/listen to Pinyin alphabet songs for kids. There are many on Youtube. Once you learn the tongue/mouth positions associated with the Pinyin initials and consonants and listen to the kids' songs a bunch of times, Mandarin phonetics becomes very easy.
For example, these songs usually start by covering all the initials (the consonants plus y and w) beginning with "bo, po, mo, fo". The initials are clustered according to how they're pronounced with the same tongue/mouth position i.e. bo po mo fo are all pronounced using the lips hence they're labials and clustered together (bo po mo use both lips; fo of course uses the top teeth and bottom lip, just like English F).
The order/cluster of the initials is as follows:
bo po mo fo - labial - pronounced using lips
de te ne le - alveolar - pronounced with tongue touching the alveolar ridge right behind upper front teeth, just like in English d, t, n, l
ge ke he - velar - pronounced with back part of tongue against back part of roof of mouth, just like in English g, k, h
ji qi xi - alveolo-palatal - pronounced with the tip of tongue low, touching bottom teeth for example, while rest of tongue curved upwards towards roof of mouth
zhi chi shi ri - retroflex - tongue tip curved up and back, like pronouncing English r, and while holding that tongue position static, pronouncing English "jer", "chur", "sure", "rur" for zhi chi shi ri respectively
zi ci si - alveolar like de te ne le above - tongue tip on alveolar ridge and pronounced English "ts" for zi ci, and English "suh" for si
So these initial consonant clusters involve the same basic tongue/mouth positions, and within the clusters are smaller differences in pronunciation like nasal, aspiration, etc. Once you understand the positions and watch the kids videos a bunch of times, you assimilate the phonetics very well. There are only 5 basic mouth/tongue positions that cover all the initial consonants, and these positions are used in English as well. The only real challenging ones are ji qi xi, the alveolo-palatals, but apparently they're also used in Russian and other Slavic languages:
Korean has the hardest phonology of the 3 East Asian languages Mandarin, Japanese, and Korean. It also has the worst Romanization. Japanese phonology is easiest, with only 3 basic vowels, similar to Spanish.
Also, despite the simple alphabet, I find Korean hard to read because like Japanese much of its vocab comes from Chinese, and is often the identical Chinese word in Chinese and Japanese, just pronounced in the Korean way. But when written in the Korean alphabet it can be vague because there are so many homonyms without the visual meaning of the Chinese character and no tones hence tone marks in Korean.
One good thing though is that the pronunciation changes for the Chinese character word used in Mandarin, Korean, and Japanese are fairly regular. So if you know how a Chinese character word is pronounced in one of the 3 languages, you generally know how it will usually sound in the other 2.
I think Korean would be best written in "mixed script" similar to how Japanese is written and how it was in the last century. Korean mixed script is even better than Japanese mixed script because Korean mixed script is strictly regular: only Chinese character derived words are written in Chinese, while Korean words and Korean grammatical words are written in hangul, while in Japanese Kanji is used for both Chinese and Japanese words and pronounced in either Chinese style or Japanese depending on use and context.
I didn't find learning the Korean alphabet itself difficult at all. Korean phonology on the other hand is very difficult. Learning the Korean alphabet would be difficult if by learning it you also mean learning the phonology perfectly. But just memorizing the sound values attached to the alphabetic signs is easy.
"ㄱ -this is the letter k" - I think it's better to say that this is like the "hard g" sound, not "k", since "k" is aspirated in English. Notice that this is like the Greek gamma but in reverse, and the gamma is pronounced similarly.
"ㄲ -this is the letter g, but unvoiced (i.e., without the vocal cords moving during pronunciation). Same as Mandarin g (as 过)." - This is different from the g in English and Mandarin. It's a "harder", "sharper" sound.
"ㄷ -this is the letter t" - More like the English d, since t in English is aspirated.
"ㄸ -this is the letter d, but unvoiced. Same as Mandarin d (as in 的)." - Similar criticism as for "ㄲ" above.
"ㅂ -this is the letter p" - More like English b, since p in English is aspirated.
"ㅃ -this is the letter b, but unvoiced. Same as Mandarin b (as in 不)." - Same criticism as for the double consonants above.
"ㅈ -stands for the consonant cluster “dz”. Generally romanized as “j”, because the z sounds kind of like a j." - "J" is the best approximation. It's not a "dz" sound which is a dental sound. It's an aveolar ridge sound like "j".
"ㅉ -Same as Mandarin j (as in 就)." - Same criticism as other double consonants.
"ㅊ -stands for the consonant cluster “ts” (Russian ц). Generally romanized as “ch”, because the s sounds kind of like a ch." - Not a "ts" sound which is an aspirated dental sound. It's best as a "ch" sound, an aspirated aveolar ridge sound.
"ㅋ -stands for the consonant cluster “kh”." - Basically a "k" sound in English. Aspirated "g" above.
"ㅌ -stands for the consonant cluster “th” (not the English phoneme made by these letters)." - Basically an English "t" sound. Aspirated "d" above.
"ㅍ -stands for the consonant cluster “ph” (not f)." - Basically English "p". Aspirated "b" above.
"ㅔ -same sound as “ㅒ”" - There is no "y" sound in this. "ㅐ" and "ㅔ" are basically identical in modern spoken Korean.
It may seem silly, but a good way to get Mandarin phonetics down is to watch/listen to Pinyin alphabet songs for kids. There are many on Youtube. Once you learn the tongue/mouth positions associated with the Pinyin initials and consonants and listen to the kids' songs a bunch of times, Mandarin phonetics becomes very easy.
For example, these songs usually start by covering all the initials (the consonants plus y and w) beginning with "bo, po, mo, fo". The initials are clustered according to how they're pronounced with the same tongue/mouth position i.e. bo po mo fo are all pronounced using the lips hence they're labials and clustered together (bo po mo use both lips; fo of course uses the top teeth and bottom lip, just like English F).
The order/cluster of the initials is as follows:
bo po mo fo - labial - pronounced using lips
de te ne le - alveolar - pronounced with tongue touching the alveolar ridge right behind upper front teeth, just like in English d, t, n, l
ge ke he - velar - pronounced with back part of tongue against back part of roof of mouth, just like in English g, k, h
ji qi xi - alveolo-palatal - pronounced with the tip of tongue low, touching bottom teeth for example, while rest of tongue curved upwards towards roof of mouth
zhi chi shi ri - retroflex - tongue tip curved up and back, like pronouncing English r, and while holding that tongue position static, pronouncing English "jer", "chur", "sure", "rur" for zhi chi shi ri respectively
zi ci si - alveolar like de te ne le above - tongue tip on alveolar ridge and pronounced English "ts" for zi ci, and English "suh" for si
So these initial consonant clusters involve the same basic tongue/mouth positions, and within the clusters are smaller differences in pronunciation like nasal, aspiration, etc. Once you understand the positions and watch the kids videos a bunch of times, you assimilate the phonetics very well. There are only 5 basic mouth/tongue positions that cover all the initial consonants, and these positions are used in English as well. The only real challenging ones are ji qi xi, the alveolo-palatals, but apparently they're also used in Russian and other Slavic languages:
https://en.wikipedia.org/wiki/Alveolo-palatal_consonant
This is a good Pinyin alphabet song:
https://www.youtube.com/watch?v=b9Ayvjy-Dgs
There are also Pinyin alphabet songs in the tune of the English ABCs song, which may be easier:
https://www.youtube.com/watch?v=EReU1BKtAXo
Korean has the hardest phonology of the 3 East Asian languages Mandarin, Japanese, and Korean. It also has the worst Romanization. Japanese phonology is easiest, with only 3 basic vowels, similar to Spanish.
Also, despite the simple alphabet, I find Korean hard to read because like Japanese much of its vocab comes from Chinese, and is often the identical Chinese word in Chinese and Japanese, just pronounced in the Korean way. But when written in the Korean alphabet it can be vague because there are so many homonyms without the visual meaning of the Chinese character and no tones hence tone marks in Korean.
One good thing though is that the pronunciation changes for the Chinese character word used in Mandarin, Korean, and Japanese are fairly regular. So if you know how a Chinese character word is pronounced in one of the 3 languages, you generally know how it will usually sound in the other 2.
I think Korean would be best written in "mixed script" similar to how Japanese is written and how it was in the last century. Korean mixed script is even better than Japanese mixed script because Korean mixed script is strictly regular: only Chinese character derived words are written in Chinese, while Korean words and Korean grammatical words are written in hangul, while in Japanese Kanji is used for both Chinese and Japanese words and pronounced in either Chinese style or Japanese depending on use and context.
https://en.wikipedia.org/wiki/Korean_mixed_script#Examples
I didn't find learning the Korean alphabet itself difficult at all. Korean phonology on the other hand is very difficult. Learning the Korean alphabet would be difficult if by learning it you also mean learning the phonology perfectly. But just memorizing the sound values attached to the alphabetic signs is easy.
"ㄱ -this is the letter k" - I think it's better to say that this is like the "hard g" sound, not "k", since "k" is aspirated in English. Notice that this is like the Greek gamma but in reverse, and the gamma is pronounced similarly.
"ㄲ -this is the letter g, but unvoiced (i.e., without the vocal cords moving during pronunciation). Same as Mandarin g (as 过)." - This is different from the g in English and Mandarin. It's a "harder", "sharper" sound.
"ㄷ -this is the letter t" - More like the English d, since t in English is aspirated.
"ㄸ -this is the letter d, but unvoiced. Same as Mandarin d (as in 的)." - Similar criticism as for "ㄲ" above.
"ㅂ -this is the letter p" - More like English b, since p in English is aspirated.
"ㅃ -this is the letter b, but unvoiced. Same as Mandarin b (as in 不)." - Same criticism as for the double consonants above.
"ㅈ -stands for the consonant cluster “dz”. Generally romanized as “j”, because the z sounds kind of like a j." - "J" is the best approximation. It's not a "dz" sound which is a dental sound. It's an aveolar ridge sound like "j".
"ㅉ -Same as Mandarin j (as in 就)." - Same criticism as other double consonants.
"ㅊ -stands for the consonant cluster “ts” (Russian ц). Generally romanized as “ch”, because the s sounds kind of like a ch." - Not a "ts" sound which is an aspirated dental sound. It's best as a "ch" sound, an aspirated aveolar ridge sound.
"ㅋ -stands for the consonant cluster “kh”." - Basically a "k" sound in English. Aspirated "g" above.
"ㅌ -stands for the consonant cluster “th” (not the English phoneme made by these letters)." - Basically an English "t" sound. Aspirated "d" above.
"ㅍ -stands for the consonant cluster “ph” (not f)." - Basically English "p". Aspirated "b" above.
"ㅔ -same sound as “ㅒ”" - There is no "y" sound in this. "ㅐ" and "ㅔ" are basically identical in modern spoken Korean.