EDIT I ascended my main, and then switched my main and hireling. Now when I go to choose a level, I can only go up to 70, when was about when I changed to challenge maps. Unfortunate. (When I'm on my main I can select even those levels I used a challenge map for.
Lesson: Do your first run to 200 without challenge maps.
I've just returned to the game after a couple years away (starting with new characters). I've been leveling on challenge maps for more xp, mobs, and loot. But I'm reading these forums and seeing something about ascending and perks. I don really understand it, but am I going to have to redo all the levels I've done using challenge maps? I'm at about level 150 and been doing challenge maps since about 80.