If you know you are going to be a life-long quilter, then you're going to need a set-up that can grow with you because expand is the name of the quilting game.
First thought...have a basement or 3 car garage for the day that you'll decide you need a long arm. Be sure it's a pleasant place to be.
Now... you need a good cutting surface with room to spread, a sewing surface deep enough to push a quilt around on, a free wall for a design board (that's imperative!) and another wall for stash storage (so something like tall bookcases with doors to close and hide the fabric.)
You can actually use a door and two filing cabinets for cutting and ironing, as well as filing patterns, etc. The main thing is you need SPACE to walk, move easily between your cutting table, sewing machine and ironing board. If you settle for a closet area it will end up becoming very frustrating.
And you won't like being upstairs and away(loft.) I had my own sewing room upstairs away from the family and I literally didn't sew for two years...just didn't like being so isolated.
So, while you're lucky enough to be able to "shop" this for yourself why not sketch out some sewing areas on graph paper and get an idea of just how much space you need? I am in a 12x12 BR and I have a very efficient space but I would BLOW out the wall to the next bedroom and spill over if my husband would let me. Good luck and keep us posted.