I've only been lving up Vaan, Ashe, and Basche.

It's weird because it doesn't lv up the other characters as I go through the game like it does in FF7.

I hope it's not gonna be like FF8 and have some parts in the game where I'm forced to fight with Balthier, Penelo, and Fran

Your not going to be forced to fight with certain characters at any point in the game once you get them all. I level up only three characters, and have the other about 10 levels under.

I look at it this way: Level 3 characters to high levels so they compensate for the others, or level all of them so they are more even.

Example: Go into the story line with 3 leveled up characters, if you are supposed to be around level 50 going into the mission with all six, make your 3 main characters level 60.

Its all in your opinion whether to level them all up or just three.

I managed to get through the storyline with just Vaan, Basch, and Ashe. Leveling up 3 characters is no problem at all.

It's okay but I suggest leveling up the other characters a little bit for back-up.

Everyone plays differently--my top three characters are definitely at higher levels than the other three, but I'll still take the time to train the lesser three whenever I can so they won't be completely worthless in case all of my top three get wasted.

My first game, I just leveled up 3 characters. I didn't even bother to mess with the others at all. They ended up being like level 13 & 12 & 12 I think. The others were like 70 But my second game, I leveled up all closely

I'm currently playing a game with a party of 1 yes one character and it's Vaan, so far I have had no problems and I'm at the gate scorpio you know in the great crystal place.

I don't advise it.I feel you are missing something by only leveling 3 characters, plus your 3 could get koed in a major battle and you wouldn't have any backups.I level all of my characters.

If you're incredibly patient then by all means go and level all your characters. But if you're quite lazy like me then sticking with just three is fine.