If you're doing all MSQ and sidequests as you go, you will be able to take one character though the story comfortably. Though I'd suggest being maybe two levels ahead of the current quest level. Once you have that lead, you won't lose it. Even more if you're doing daily roulettes as you go.
If nothing else, move on when you're Lv67-68 or something so you can at least get some value out of quest leveling.