The best character is always whichever one feels most natural for you. Tier rankings and match ups should always come second to that.
I don't suggest choosing characters because you like them in other games or even just in general. When playing you won't care you're playing with your favorite character, you'll be frustrated with a lack of approach options or something like that.
I also don't suggest playing for the money. I'm in college too, so I get it, but play to have fun or you won't succeed.
As for hitting in the air, part of it is your main. Charizard and Bowser have pretty bad air mobility while ZSS can sometimes move too fast for people not used to it. Training with it's time control is a good place to practice this.
My biggest suggestion is to go back to the basics. Play each character until you can consistently 3 stock level 7 computers (yes level 7, not 9 or 50). Once you've done that, pick the 5 or so characters you enjoyed playing the most and read through their character discussions. After that, start practicing of Online (preferably via NNID exchange, but FG works too). Once you feel pretty confident there, you're tournament ready and just need experience. Follow this, and you can be a top level player in just a few months
