I used to abuse the easy level up trick you could do with bannon early in the game. Just set the commands to memory, edgar auto xbow, bannon health, and terra and sabin fight. Get to the raft part before you fight the octopus, and using a turbo controller, just tape down the confirm buttom. You keep circling around one junction point, and enemies will keep attacking you. A few hours later and you're generally so overpowered the rest of the game is cake. I always giggle hitting the stupid octupus with fire dance and fire 3 at the start of the game.
As for the Tower of Fanatics, bring wall rings and have berserk and rasp/osmose for the last battle. Equip everyone with wall rings and your invincible for 99% of the area. At the boss, hit him with berserk, negating all his spell casting cuz it will heal him on occasion, then just rasp and osmose him til he's out of mp. He'll attempt ultima, but flop cuz he's got no mp, and you win. Also a possibility, learn life 3, which revives you after death, and cast it on someone, then tear him apart, though you'll still want berserk on cuz his physical damage is garbage. His ultima will generally kill anyone under max hp even with shell on. Could also try golem I guess, never did though, cuz rasp/osmose is just so easy.