Something else to think about is where you want it. I was using the finished side of our basement (about 15’ x 30’) and it was fabulous, but I didn’t like being downstairs and away from everything (“everything” being my husband lying on the couch and my dog lying on the floor). I moved my sewing room up to the spare bedroom (moved the BR to the basement) and I sew a lot more. Like my dog, I want to be with my pack.
Also, and this is probably in every sewing room post I’ve written, put stuff on wheels! Pressing tables and cutting tables can be rolled out of the way easily allowing you to customize your room when you need to.
And go big!