There is none. Except when you reset quests reset with you so you can earn the crystals all over again
What kind of stats do you need to make the lady few quests not "extremely difficult"? I'm on "demon temples" (sorry about bad spelling) and it's tough. The hardest quest that isn't that hard for me at full army is the first one that always gives you 1mil. How many for buildings do I need to make them easier?
I'm sorry I haven't checked here in awhile I'm not sure if there's a "best build" for quests. I personally think that after a certain point (maybe 20 forges? I'm conpletely hazarding that guess), it becomes more strategy than stats (strat over stat). I used a quest twice, regen, repeat strategy for the last quest and I finished in a week. With 22 land.