I agree with Jaciquiltznok [hope I spelled that correctly.]
Start with local talent. Some groups may want to provide their own leader for their retreats ... and that is OK too. Once you are well established you can then offer more experienced talent for your retreats.
Check for zoning, parking, water & sewer facilities [we women do take a toll on septic tanks and water usage] , electrical capability, lighting, wall space for displaying projects, ironing boards and irons. Storage space is a must as is good tables and chairs ... or at least pads for the chairs. A comfortable area for those who want to relax or do handwork in quieter surroundings.
Adequate insurance coverage is must. On one of our retreats someone burned the carpet with her iron. No one 'fessed up and I think our group had to pay for damages.
Then there is the matter of food. Does each group provide their own and have space in the kitchen for refrigeration, prep, and cooking. Or ... will you provide meals for a fee. Then you have to consider cooking for special diets: lactose free, diabetic, salt free, caffiene free, food intolerances.
Small groups vs larger groups. What sizes can you accomodate. Can you do 2 separate small groups that are not occupying the same creative space?
What type of contract do you envision having for groups.
What choices? Deposits and are they refundable before a determined date for certain causes. This includes asking if the group has it's own insurance for retreats, as many guild have this in place. Or maybe agroup can purchase a one time policy for each retreat.
Then another biggie: do you have community [neighbors as well as quilters/artists] support.
Do you have a means for providing good publicity. Will you publish is a local paper or something like The Country Registrar, or LQS's. Can you have a web site and maintain it ... or hire someone to help you with this.
Lots to think about and do.
Good luck.
ali