Hi, i havent played this mod and am waiting till version 2. So heres a suggestion that may be already implemented:
For the HRE one could make it more historical and harder, that one has to go to rome (instead of the capitol) to get the title Imperator romani and the coronation by the pope. That how it was until the 15th century. One has to make ally with fight the way through the northern italy - thats how it was historically pretty often - to get to rome.
and the rex germanicae was normaly the heir and he has to be crowned in Aachen (one could take cologne instead). For this, one has to control the 6 electorates (after 1350) or at least mainz and cologne (before).
If some more suggetions are needed let me know..