Do you think TTMIK is good for a beginner who has mastered as much Hangul as capable? I know there's the typical "learn some vocab," "learn verb conjugation," "learn sentence structure" after Hangul, but what are good sources? How do we know one is reliable? Should I follow TMMIK?
Well I personally didnt use TTMIK as a beginner (cause they didnt exist then lol) so I cant speak from first hand experience but I think they are great for grammar because they have visual and audio components. (Although if I remember correctly some of the earlier courses were just a looot of the hosts chitchatting so maybe the pdfs are better.)
Theres never any sure fire way to know if a source is reliable, but if you wanna be SURE then pull from a source thats made by native Korean speakers in Korea (like ttmik) because odds are they wont make mistakes in their own language.
When it comes to vocab, you can always make your own vocab lists by picking the words you dont know out of korean songs/tv shows/ websites/ movies/ etc. This is how I’ve learned from the beginning (and how I run my blog) and its great because when you have to find the english meanings yourself by reading lots of example sentences the words stick to your memory much easier (and youll have already seen them in context in your source material.)
Theres no need to be super worried about unreliable sources, just make sure youre pulling from lots of sources when learning because the wider your scope, the more likely youll be able to spot inconsistencies. Good luck!