RTF is a global modification that replaces all towns in the game.

maybe we should give the Necromancers a castle from Heroes 6? :D

In my opinion, the Necromancer castle in Heroes 6 is terrible. The only undead unit that I liked there was the skeleton throwing spears.

It can be implemented, and there's even a mod for that! But it all depends on the starting faction, not the hero.

Aren't heroes tied to their faction in any way? Then it's more difficult, but still possible. If you check the hero's name.

I have an idea for upgrading the tavern: in the menu for hiring a new hero, a button appears that, for a small fee (e.g., 250 gold), provides two other random heroes for hiring.