My questions are twofold:
1) When and where should leveling the party to level 99 be done?
2) When and where should completing the License Board (except for some Espers, naturally) be done?
I've discovered that allies will be recruited at levels commensurate to the present characters, so if I leveled Vaan and Penelo to 99 before I recruit anyone else, they'd all already be at 99. Same deal with LP.
In addition I found that with three party members (and a guest) get half the experience that just Vaan and Penelo did fighting the same monsters. So again, it would seem leveling early would be an advantage.
Right now I leveled Vaan and Penelo to level 34 and filled in the top of the License Board completely. Took me 60+ hours, but I spent a lot of that time fighting weak foes for LP.