A Victorian house probably would not be my first choice for a quilting retreat unless it had an elevator. Many of us quilters do not enjoy hobbling up & down the stairs, especially on a vacation. As others have said, space to do handwork, plenty of outlets for at least 6 machines and 2-3 irons (and the amperage to support those outlets). A couple of bathrooms minimum & plenty of hot water (honestly! I'm quilting, not camping). Family-style dining or restaurants within 15 minutes drive. Nearby LQS for emergency supplies. And depending on the price, some sort of quilting personality/instructor. If it is a low-budget/grab-your-quilting-friends type of place where you just go to have a serene environment & place to quilt you won't need as many things as a draw, but you'd still need to make sure people had basic comforts and access to quilting supplies. (I'm blessed to be in a large guild where people offer their lake house for free & we just need to bring the food and our supplies; those are only 200amps so we get one iron and 3 machines & that's about all the load it can handle. It's not ideal in that sense, but other than us feeding the hostess and helping put the house back in order at the end of the long weekend, it's free so I wouldn't dare complain. It's a beautiful home in the woods on a lake that is nicely decorated & has a couple restaurants nearby and an LQS about 20 minutes away. It's one story with plenty of parking.
For a true quilting retreat that costs a few hundred dollars, I personally would want to know that a quilting instructor is coming who will be teaching some technique in which I'm interested. Of course then you would need even more outlets unless you're only catering to Jinny Beyer-types who do everything by hand.