Yes, this would be a good plan. Also, just wait until you don’t have Squall in the party at some points. Then run around with those characters to level up.
… like when your party splits into two parties in ultimecia’s castle.
Hah, I think that would be a little late. I like to get all my characters to 99 before disk 4. There are other times that the characters split throughout the story.
It doesn’t really matter, though. Just keep them with Squall and they’ll eventually catch up. If you keep switching them to level them all at once it will happen. I usually just keep a certain two characters with Squall the whole game. It forces you to switch it up now and then and I’ve never really had a problem. Just play and it shouldn’t make too much of a difference.