I had a pretty crappy roster and managed to do it a in March. I would say you should be fine until the collector. Everyone gets wrecked by his special attacks unless you can dex them. When you use your revives on him don't even bother with the health potion, one hit with a special and your dead anyway. save the health potions for the fights leading up to him. That's the basic strategy I used and managed to do it on a whim. I maybe spent 200 units as I didn't have very many revives.