If I could do it over again, I would learn Chinese before Korean or Japanese. My Chinese friends who learned Korean learned it way faster than any western learner.
Japanese students learned Korean even quicker than the Chinese students - in addition to using Chinese words, Japanese and Korean have the same grammar structure ( Subject Object Verb ) whereas Chinese and English are different (Subject Verb Object)
Learning Chinese is like learning Latin before learning a Romance language.
The added benefit is that Chinese isn’t a dead language.
Both Japanese and Korean are distinct from Chinese and beautiful languages (I really do love Korean, such a pretty, logical language), but China has been an influence in the region for so long they can’t have help absorbing and using pieces of the Chinese languages.
Fun random fact: a lot of Korean words are built on Chinese words; however, some of those words were taken from Chinese thousands of years ago.
The Chinese pronunciations have changed. Some researchers have been known to use Korean pronunciations of words to help triangulate to what ancient Chinese characters would sound like (in combination with poems where you know what rhymes to expect etc)!