DISCUSSIONS on “Rules for online games in HoMM3 and formulas for calculating player rating.”

Multiplayer was already present in the second Heroes game, and I believe the standard balance proposed by the developers is good and doesn't require any changes.

As for the vampire upgrade, you could introduce the following restriction: it can only be built after all other Necropolis buildings have been constructed, and the Stronghold, of course, would be the second-to-last building in that case. Daily saves exist, so no one can cheat with this. If you calculate approximately, it will take until the middle to end of the 4th week.