First question

Zidane-The Tower's more than enough unless you really want to get Ultima Weapon.I beat the game with Zidane equipped with an Orichalcon(the one bought in Terra).

Dagger-Eiko's better at healing,but if you like Dagger more,it's up to you.

Vivi-No problem,just equip Reflectx2 ability.

Freya-If your Dragon crest can do 9999 damage then use it.If not,go for Dragon breath and Cherry Blossom.

I strongly recommend Amarant for his Chakra skill that can heal your HP and MP.He acn attack and supprt at the same time so he's my best character in the game.DO NOT equip healer on him.It heals the enemy when you attack.My party is Zidane,Vivi,Eiko and Amarant.

Abilities-Anything that includes healing(eg. auto-regen),status immunities,increasing HP(for enduring) and MP(for magic) and some like the others told you.What's locomotion anyway?Never used it so I don't know,can anyone tell me?

Level-40+ should do the trick.Unless you'e confident of entering at 40- go ahaed.

The bosses really aren't that hard,except for tiamat(second boss) which drain your stats,which you will preferably counter with a fast battle.Maliris(first),keep your HP high AT ALL TIMES.Maliris attacks you after you kill him/her which deals quite a kick ass damage.Kraken(third),Don't care about the tentacles,kill the body and you win(if I'm not mistaken).Lich(fourth),try equipping auto float to counter his earthquake attack.As for death,just make sure that your character's level aren't multiples of 5.

Deathguise-Steal the Duel Claws from him if you don't have one.Then,just feed him his own arse.

Kuja-keep your HP high.That's all.