Welcome.
Can you get the seller to give you the dimensions? Personally, I would wait until I had it in my possession before ordering a sofa and take careful measurements and think about your approach (how to get it in the door, how to mount it).
Second, the slide - you mentioned it's well kept, but IMHO that would mean a working slide. There could be a host of reasons why it isn't working - bad batteries, bad motor, loose ground, etc. This could be a very small problem or a very big one. I would never touch an rv with slide issues. Too many used units out there without this potentially costly issue.
Your TV and AC are on different circuits. Your TV is usually on 12V and your AC runs off 120 powered by your generator or shore power. You may want to brush up on the 12V side of life, your batteries and capacity and how your different things run on different power sources.