That lift would not have been of much help to me during my M3 rebuild. While most of the actual work took place forward of the lift, my body would have to lie right in the path of the base of that thing. And I shudder to think how we would've installed the transmission with all that stuff in the way, or work on the driveshaft. That said, not many people do this sort of thing at home.
This should be fine for oil changes, some moderate suspension work, that kind of stuff. If it were my garage,though, I'd save for the two-post.
Regarding washing indoors -- I did this once in February in my two-car garage, which had no drain and no hot water. It was not a problem. The trick was to be careful with where you aim the hose, and to generously flush the garage floor afterwards. Most of the water flowed out the garage door naturally, but I had to do a little clean-up with a push broom.