Oooo Seravin, I like that idea. At least the Erinyes was moving up the social ladder...and would have certianly caused all kinds of politcal fallout had that continued.
I think the important aspect of a stronghold is to make sure all of the PCs have something to get their hands into. Sure, the paladin or fighter generally gets to run the things over-all, but we still have a mage, priest, and thief to worry about (yeah, simplifying things a little here).
Obviously, the priest will want to build a shrine or church there. Perhaps he finds some old catacombs when he starts to dig out the basement or a small plague starts running through the area...people always look to those priests then, don't they?
The thief might wish to start her own guild or perhaps go into the legit (or semi-legit) trading business. What other merchants or thieves will be really happy about that?
The mage...well, he's bookish and generally only interested in his magical research. Of course, he'll have to set up a lab and library, which means gaining supplies. He might have to make use of the rogue for some of these things while other things might require some summonings and other means of information gathering/diplomacy.
Those brief blurbs aside, you also have to make the PCs enjoy there they are. The cook is not the cook, but Beatrice, a halfling cook who's son has recently joined an adventuring party and she constantly worries about him, perhaps even going so far as to ask the wizard to scry him for her or issue a Sending.The stablemaster is Yorrin, a man good with the horses and hisjob, but has a tendency to gamble and drink a little too much. Half the time, he's late to his duties and might even be skimming a little of the money to pay his debts. These little things can always lead into all kinds of fun adventures but they at least add a flavor of realism and might even make the PCs start wanting to pull their hair out (something I think a lot of nobles wanted to do back in the day).