Joseph, Rikku's base h.p is 360, not 320. Just train her a little bit and her h.p. will skyrocket. Don't worry. Just set goals on the sphere grid for 3 CHARACTERS. THREE. (For example: have Yuna learn Holy before fighting Yunalesca, have Auron learn Armor Break before Evrae, etc.) I recommend using Auron, Tidus, Yuna, and sometimes Lulu (until she learns flare) for the rest of the game. Don't focus on side quests yet either, just get into the game.

Tav, how is he screwed? If anything, overleveling is good.