My tips and advice

I originally typed this up as a reply to someone who wanted to learn how to speak JP, KN, and CN, and it was too long to waste so I think I'll post this here to help anyone out.

On speaking: If you're going to learn Japanese and Korean, learn the alphabet. Japanese always ends in a vowel, and Korean has those double letters like "ae" and "eu" (thats how i distinguish the two languages). Japanese and Korean grammar is alike. Japanese uses particles like "-wa" or "-ga" to mark the topic and a "-o" to mark the direct object. I hear Korean does the same (with different particles). On a language family tree, Japanese and Korean /may/ have closer roots to each other than to the chinese family, even if they do borrow some vocab.

(Edit: Just remembered to add a note on here that North Korean and South Korean are pretty different, because South Korea has borrowed many foreign words, but North Korea continues using traditional Korean as there is little outside influence)

For Chinese (there's many dialects, but definitely learn Mandarin. Everyone in China will understand Mandarin, but likely not everyone will know other dialects), learn the pinyin and tones. You can find them online. Good tone pronunciation is what differentiates a native and foreign mandarin speaker. Chinese is also different in that there's different grammar rules, but I think it's relatively similar to English in that it uses subject-verb-predicate.

On reading/writing: I don't know Korean, but I'm a native Chinese speaker and I'm studying Japanese so I can help with that. Japanese indeed uses kanji, which are basically chinese characters, and it has two pronunciations kun-yomi(Japanese pronunciation) and on-yomi(original Chinese pronunciation) this is why i believe it will help to learn Chinese if you are also learning Japanese. (Though the meanings of the characters are a little bit different, most of the concepts are the same. For example- 恋人 in Japanese means "lover" but in Chinese means "mistress")

For Chinese, learning to speak it is so much easier than learning to write it. Especially if you didnt start out early learning the hanzi (characters). To be even a little fluent you'll need to learn approximately 3000-4000 characters (and there are tens of thousands total). It's not like Japanese and Korean, it doesnt have an alphabet system. Chinese has two different writing styles, simplified and traditional.

Traditional is the old way of writing characters, and it's more complicated because each character represents one single word. Today, it's only used in Taiwan, Hong Kong (HK uses Cantonese dialect, so they have their own unique words as well), and overseas, like in Chinatowns. Simplified was created after 1949 to make traditional characters easier to write (example, 學 to 学) it is used in mainland china. And I think Kanji is mostly in simplified Chinese as well, because after WWII, they simpified the characters (though they might still use some traditional characters, since they did it independently and didn't work together with China to do so) *EDIT: Some kanji, such as 学, were simplified, but after looking around, I now believe most are still traditional.* There are some Chinese manga raws that use simplified, and some that use traditional, so I can't say which one is better for that. It shouldn't be too hard to learn both if you know one though.

Some tricks I use to learn hanzi: look up "radicals" because I primarily use those to determine the meaning of the characters. (For example, 白 means "white," but add a heart radical next to it and it becomes 怕 which means "fear". The way I interpret this is that white is an unlucky color in Asian culture representing death, and there is a heart radical because fear has to do with your emotions, or your heart.) Also some words have similar pronunciation if they have the same characters in it (like 怕 "fear" and 帕 a part of the word "handkerchief", both have 白 in it and are both pronounced "pà").

Learning new languages can help you express yourself in different ways, especially because there are some words in these languages that English does not have. Good luck!