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.

Another show in February that might work for you.

http://www.pslcrazyquilters.com/2018-show.html

Check out the vendor list. Good luck on your decision.

You need about 2 feet on each side and at least 3 feet front and back. I am a size 10 and I need that much room to get around. You might be better off with the smaller frames they make now.

I spoke to an Innova dealer today and she said they can make a 9 foot frame- but I do want to be able to make a queen top- that being said, she also said they can put casters on the frame to move it around so I can get behind it to do pantos etc. I can move it on an angle to get behind it. I have plenty of space for the width. I really need to physically see one in person to measure and picture it exactly- not by what they recommend since everyone has a different opinion. I did remeasure and the room is a few inches bigger than I thought! I think I see a big diet in my future to move around lol!

Thanks Rhonda- My guild Seaside Piecemakers has our show in Melbourne in Feb also- not too far from PSL!!

I bought my Gammill used--it's a 2006 Classic Plus with a 26" arm & 14' frame. I have to honestly say that I rarely do a king size quilt (who can afford that much fabric!), but it' is nice to have the larger frame to load quilts lenght-wise. that being said, I also don't think the larger throat is that useful either--who has arms that long!!?? I do think the height of the throat is important so that you can roll a longer quilt.
My friend with a 12" Gammill frame put her's diagonally in her room and since she was small, could easily walk around the one end and work on both sides. her quilting room was probably not a whole lot bigger than your's, so I'd suggest you measure diagonally and see what your space is there.
Having your frame on wheels is awesome! Especially since I got laminate flooring. Just make sure those wheels include good brakes on them.
As far as a saddle stool--I suggest you try out both one of them and also a drafting stool. I've had both knees replaced and found the saddle stool a little hard to get on due to my stability issues--the drafting stool doesn't require me to "throw" a leg over like the saddle stool did.
Good luck! I think you will really find that the long arm will help with those back problems that you experience with your sit-down and sandwiching for it. just make sure that whichever one you choose, that it's set up the correct height for you!
P.S. Long arms heads are so heavy that you won't likely be hauling it to the dealership---so don't worry too much about proximity to dealer, but rather responsiveness to your phone calls for tech support. We become our own techs on a day-to-day basis with tech support. Most send their techs out long distance and the calls are expensive--so rarer!

Check out the Innovas. A smooth running machine. Google Innova and you should find a lot of info. Don’t buy anything without trying them. When you try various brands you will feel the difference in how they ha e and the smoothness of the operation. Try them all not just named brands

I purchased used and have had great customer support My friend on the other hand got brand new and her support sucks

Just wanted to mention that if you have back problems, I would suggest you look into zippered leaders. You can sit to put zippers on or off so you only spend a few minutes zipping on or off the table. Also, you use safety pins - much less chance of poking yourself(I don't think I ever have) as with the large pins. I think some people baste the quilt to the half zipper but I was taught to use safety pins which is easier in my opinion. It is a one time investment and a one-time job of sewing half the zippers onto the table leaders. Here's a link to them on Amazon: https://www.amazon.com/Zipperstop-Wh.../dp/B005774J2G You may have to look around for the right size for your table. Google them and you will also find you tube videos. I have found here on the board there hasn't been too much enthusiasm for them but I have used them for years and wouldn't do it any other way.
Concerning your space problem - do you have a closet in the room? I saw one person who removed the sliding doors from the closet creating an alcove to the room which allowed additional space for the long arm.

And remember, you don't have to stand at the machine for hours on end. Take frequent breaks and then return to the quilting.

Yes, you can put it in your room diagonally. I can do 120" by 120" quilts and am so glad I have a very big frame. Is there no way you can put it some where else? How about trading rooms with the master bedroom or den. How about the garage or the kitchen /dining room?