Decide what space you need for the items you now have plus cupboards to be installed, and add for future add-ons. --Then make it bigger. You didn't mention a quilting frame or longarm. This may be something you may want to have room for. I too will be planning a retirement home soon. I will include space for all my sewing needs. I use 2+ rooms in my house now. The main room is 8' X 16'. The other one is 12' X 9'. I figure with all that I have and may add, the minimum space would need to be 18' X 14'. I would like it to be bigger but cost will have to be a factor. -- My husband gets the barn. I will just need a little space for the garden supplies.