Thank you all for your very valuable input!
I am reassessing my choice based on available space. Wow! My room is just under 15x12. It's an old house and ALL the rooms are about that size.
I can put it on casters to roll to the wall when not used. I could also take down a section of the frame so it is a smaller footprint. Putting things under it for storage sounds sensible. I can clean out my closet, seal up the plaster to keep out the mice, and start using it for quilt storage instead of books.
Or I could commandeer the kids' study since they no longer live at home and have that one room for the longarm and leave it in place permanently.
Or I could reduce my ambitions and get a 'mid-arm'. Or get a bigger-throat DSM. Or re-read that 7-reason post on Leah Day's blog about why it is fine to use a DSM to FMQ until I am convinced.
Thanks all - much food for thought! Happy quilting to you all, whatever your 'ride'