I have an APQS Lenni, 20 in. 10 ft. table and it has given me no trouble. Their customer service has always been excellent. That said, I don't know about the newer machines now. They have made so many changes in the machines. I've had my machine 10 years this august and have never needed service. The tension is always good, with very little, if any, tweeking. It loves almost all threads and with that tweeking I mentioned, I haven't found the thread I can't use. It makes a beautiful stitch. It doesn't require a lot of maintenance. I'm not tall and I chose Lenni for the 20 in. throat reach. With a back problem I don't think you would want larger.
I have a saddle stool and use it all the time, even for pantos.
Whatever machine you choose (I would go with a longarm company) try as many as you can before deciding. They are not all created equal. And, of course, there is always the lemon factor.
As for space, you are kind of tight, even for 10 feet. I would not go smaller than 10. That's a lot of money for not being able to make at least a full bed quilt. If you have a double closet, maybe you could put one end of the table in there, then you could walk around the other end. Or maybe the table could be placed at an angle coming out from a corner. Just some ideas.