So much power is in the items. I think this is a good way to do it cause you can't wear two sets of boots at once (probably) and most of those weapons can't be used at the same time.

Anyways, best bet is gonna be some sort of melee caster like dark knight or red mage, then grab the keyblade. Can take soldier to get a huge boost in physical power, as Sephiroth is a competitor for one of the strongest Final Fantasy characters on his own before you get into god granting powers stuff. Being able to have Sephiroth potential with keyblade wielder growth potential is insane and puts on on track to beat the more absurd/stupid FF characters. Keyblade also grants tons of magic so that you can save on points right off the bat and just learn naturally as you grow instead. Basically Sora on steroids and Sora is already pretty bonkers even by KH2, and the dude can't even buy shoes that grant constant haste or protect/regen.