Wow! Lots of good advise. Figure out a size for each station in the room including person space: 12 ft long arm=14x8=112 sq ft, 5 sewing stations 6x6x5=150 sq ft, iron station 4x4=16 sq ft, cutting 6x6=36 sq ft, storage 1x20=20 sq ft, design wall 12 x 2=24 sq ft, etc. Be sure to add traffic patterns. I'd need some time to think of other spaces, but this as a minimum is approx 14x28.

Next figure out access to rest of house. Will you conduct business in this area? Taking customers through private spaces can be unprofessional. Going through another room can be difficult. Will it be a room addition or room enlargement. If it's part of the house, how will the additional sq ft affect existing HVAC capacities and existing electrical capacities? Do you need building permits? If yes, then you may need an architect who could help you with a lot of these questions.

3 yrs ago, we added a 18 x 18 room onto our house for my sewing room. At the time I thought it would be enough, but as time has gone by, I wish I could have gone bigger. You know the saying.."stuff expands to meet the existing space" LOL:)