First, teams. Each team will be able to need to fight independently and be able to rely on its own characters. The party will need be able to fight some bosses as well. I balanced mine out like the below. Please note I had fully completed all the sidequests in the other sections. Further reasoning momentarily.
Team #1: Celes, Shadow, Mog, Gau.
So, yes, why these? Well, Terra, Celes, and Strago were placed to be healers. Strago, remember, should've had White Wind AND Mighty Guard at this point. Edgar does nice damage with the Drill. Shadow has more elemental variety and control, as well as some nice damage. Plus, Gau and Mog were kinda low-level, so had to boost it somehow.
Cyan does some nice physical damage, as does Sabin. Gau, Rages. Come on, you knew that. Locke, well… He does nice damage AND can have some nice steals: Ribbon, Force Armor, and the Minerva Bustier for the most part. Mog… Well, given that this, more or less, is my weakest team, his Molulu's Charm came in handy.
Setzer - had to put 'im somewhere. And Relm is good with Strago to learn some Lores from the Dark Force. She can Control it and help him learn up to 19 of the 24 Lores. Granted, this is probably not the best strategy. Oh well; I'm not really going to assume team members individually in the walkthrough all too much anyways.
Yes, seriously, bring a Teleport Stone. If you get stuck at low HP, no MP, and no items, your only saving grace will be that one Teleport Stone. The situation itself is very unlikely given all the building up from the sidequesting.
Finally, if you have any plans to use Lv. ? Holy - and you should - you'll want to manipulate your Gil to have a one's digit of "1". In this way, the attack will always hit whatever it hits. (This is because all enemies here will give 0 Gil.) Any more to do? I think not. Go find Kefka's Tower and land on it.