Gilligan, you should play a tournament player.

You will most likely be completely thrashed. Of course, I would too, just cause I know almost all the techniques and know all the theory doesn't mean my actual "play" is good. I am unable to go tournaments, no active smash in my city, and lack of transportation. So I set up a tournament environment in my house and learn, but you need a real smash scene to be PHYSICALLY good.
Also, Gilligan, Up-B blows, so easy to see coming, but in casual play it is a very powerful move.
Kirby was severely nerfed in Melee, but people should use the character they are most confortable with. Although tiers tell which character will win if both players are equally skilled, that pretty much almost never happens in tournaments. If you want aerial mobility as your prime though, try Jigglypuff, excellent character, although most people thinks she sucks.