I saw some old post about putting coin in the bank. Is it still a thing? I can't find anywhere in the setting to put my coin into bank I'm kinda confuse now
Depends. If you like giving reactions to other forum members, you might want to save for P1 and get that. It includes M+ and gets rid of the reaction cooldown. If you're just in for the + games, M+ is sufficient.
Or if you are really interested in uncensored AI art, you might try to save your way up to P4 and P5. Which is what I am currently doing. But I got P1 first. Worth it, in my opinion, but your mileage may vary.