I'd want to check the electrical load on the house -- especially since you say it's old. Can it support multiple sewing machines (or would you only cater to hand quilters?)? Also, is the plumbing sufficient? I ask that having had a residential rental and realizing that some people flush feminine products and/or large amounts of toilet tissue and that can clog old plumbing -- or sometimes even new plumbing when you're on well & septic with low-flow toilets. A top-notch home inspector could probably help you figure those things out ... or direct you to someone who could.
Also, do you have plenty of space for parking for your guests if they don't carpool? And you may need to look into the laws in the area about accessibility. Often older buildings are exempt until they have to pull permits to update something (electrical, plumbing, windows).
I agree with the person who suggested checking with the local SBA. The Chamber of Commerce & State Tourism Board may also be useful resources. And definitely, definitely talk with your insurance agent. People do all sorts of crazy things in general & when you add in sharp needles, rotating blades and very often, elderly clientele, it is too high of a risk to carry on your own; regular homeowner's insurance typically will not cover damages resulting from running your business (on top of fire, flood or whatever else could happen).
And finally, you want to consider where you will live. Would you live in the retreat house? In a home nearby? If you're going to live on-site, how will you create a space for yourself/your family? Who can help you take care of guests if you are sick or injured? What resource people do you have in your network that could help with the legal, financial, marketing & managerial aspects of the business?