I painted the whole interior of my house. I had a little help from a friend. I can tell you it is more difficult if you have a bad back. Especially when painting the ceiling.
Having a roller with a long handle will definitely ease the stress on your back especially when painting the ceiling. With this long-handle-roller, you don't need a ladder to paint the ceiling (just stand on the floor and you can reach the ceiling with the long handle).
Another difficult part is painting the edges of the walls or ceiling where two walls meet. Especially if you have already painted one of them and both walls needs to be painted different colors. To have clean paint edges, I always tape off the side of the already painted wall to avoid messing it up. Same thing for painting around doors and windows.
Heads up when taping off!
1. Don't try to tape off on wet paint.
2. Don't let the tape too long on the wall. Because it may pull off with some of the wall paint when you are taking it off. This actually depends on the type and quality of the tape you are using.