Regarding secondary castles... Has anyone seen a map with more than two castles of the same faction? I haven't either. You'd have to create such a map yourself. And if the castles appear randomly, then Necropolis might lose the bonus to magic power, but it can gather undead from the secondary castles. Again, the army will be huge. What can Orc do? You can, of course, send everyone to the slave market, but there are no problems with money on large maps. You can also hire "foreign" heroes, but there won't be enough experience for everyone. But Necropolis can have a mentor.