I'm with ragamuffin, the BIGGER the better....I'm of the notion that you just can't get too big because it will get filled up....and that way you can have storage for a lot of stuff! I have a sewing room that's 15.5 x15.5 and an attached walk-in closet with double-doors that open up that's 15.5 x 7, and even at that I could use more space!!! Since you do all of those other crafty things and sew too, and if you can afford it, I'd set up rooms or spaces for each craft in a separate area. That way, you wouldn't have to get things out and put them back when you are working on other projects. I'd also build a restroom (add plumbing stubs for a shower, even if you don't install at that time) and kitchenette area with a MW, TV, fridge and have a phone, computer and all the amenities that's in your house. Then if at some point you sell or can't do any of it any more, it can be converted into a guest cottage or MIL house because everything is there....