That totally sucks about the body shop butchering your car. I firmly believe you have to know the owner personally to get a quality job done on your car. My best friend's dad owns a body shop in town, and he is like my second father so I get lucky when it comes to major body work on my car. I do like to do as much of the work as I can myself so he has coached me through a lot of it.
Using a buffer shouldn't be over complicated. What I would recommend is to either 1. go to a junk yard and get some panel off of a junk car that has some decent paint, and practice on it to get used to the buffer. OR 2, get a super super super soft pad, and practice on your car by just using a very non aggressive polish or wax. This will not get the scratches out but give you a good opportunity to get used to how the buffer feels and works with out worrying about damaging your paint.
Then I would follow our steps from above. Also I would be sure to start with the least aggressive method that will work. Since its your first time, I would determine the step you think will do the job, and then start with one a step less aggressive. It is easier to try again if you weren't aggressive enough, than to try and fix a too aggressive method.