I turned my dining room into my sewing room. It is roughly 11'x15', with 3 machines in cabinets, a Featherweight card table, and a serger on its own table. My grandma's china cabinet, a book shelf, and a folding cutting table is in there as well. It is not enough space. My home is an open-concept so right around the corner in the livingroom is my Singer 301 and my ironing board gets set up along the staircase going up to the loft. There is a small pressing table between the Featherweight and my treadle machine. I suppose if I did not have as many sewing machines there would be more room, but where is the fun in that! LOL
Go as big as you can, especially with a long arm.