I was gonna suggest levels for the areas so here it goes:

Rabanastre - 4 / 4
Waterway - 5
Palace - 5(No battles here)
More Waterway - 5 / 6 / 6
Gaurds - 6 / 7 / 7
Firemane - 8 / 9 / 9 / ?(Guest Level)
Nalbina Dungeon - 8 / 9 / 9
Barheim Passage - 9 / 10 / 10 / 11
Estersand - same as Passage
Lhusu Mines - 11 / 12 / 12 / ??(Basch, I'd keep him lowest level possible._.)
Leviathan - 12 / 13 / 13 / ?? / 14 and thats it.