You should get intel report as high as possible. You cannot see the wall health until intel report 10, and there are times that can hinder a rally, particularly one where the leader is reaching. Again, these are all 'back of the napkin' estimates, mileage may vary. 5s most of the time require a full 25 BH, usually with some T4. 4s require a good leader and 1 mil or so troops, up to 2.2 mil for hard nests. 3s are where you start needing a better leader, but could be down with 200-300k if the leader is good and nest is easy. Lvl 2s probably could be done with 50k T3 for a decent rally leader, more to compenstae for a worse leader. You can do lvl 1s with as few as 20k T3 with a bad rally leader (I have done so on an alt that I auto-selected the heroes and didn't change gear/talents).Some back of the napkin estimates, assuming you send middle of the road heroes (right type, middle quality):
