I found a neat trick with griffins and time back. Let's say your leadership allows 100 griffins. Enter an easy battle with 66 griffins, split them and use time back. That way you'll have 66+33=99 griffins, and you will still have that many after the battle is over. A lot easier than using sacrifice.
I'm considering including black dragons. I believe I can heal them with the quested AE heal Life Light, I have 5 eggs already, and if I learn the diplomacy skill I can get more of them. Vampires and skeleton archers are not good against the undead, dragons will be good replacement. The skill is a bit expensive though.
I wonder how hard would it be to play without sacrifice in addition to not buying units. Maybe it's also possible even on "impossible". At least if you find "resurrect" early enough
and allowing buying unit containers could get you a solid starting army.