I agree with what is being said here...focus on one job at a time (wish I took my own advice ).
We did the floors in our own house. It really depends on what kind of quality you're looking for. Our floors are Fir, and they were painted with several coats of gray porch paint (some of them). We did ONE room at a time (for the most part). Is it back breaking hard work?...YES! Is it rewarding to do it yourself?...ABSOLUTELY!
We weren't sure if we should tackle this one ourselves, but decided to try. It wasn't about the money for us, but rather the experience, and the satisfaction of knowing we did it ourselves. We used a drum sander and disc edger. The drum sander is actually a "belt" sander, which is easier to use and is much more forgiving than the old style drum. We went through LOTS of belts and discs...starting with 25 grit.
We finished with a sealer and wax. No poly on the floor. Our neighbors have the same type of flooring we have. They hired pro's. It went much faster, and of course looks better...
I'd say give it a try. Rent one, use it in a room where it's not going to matter much. If you find it to be too much, then hire it out. Just my two cents...
Here's a couple of before/during/after shots of our floors. (not actually in any particular order...I can't get this attachment thing right)