Yea. Someone not educated in the autobody business has no place doing any sort of prep work. The paint job comes out the way it does 90% becaue of the prep work. Obviously with spraying, you dont want runs, dry spots, or orange peel but thats the easy part and the fixable part. Once you paint, if you see dents / scratches.. your going to either have to suck it up or paint it again. With wet sanding / buffing, you can repair paint most of the time. If you have to ask how much hardener to mix with the bondo, you shouldn't even be trying it
Nothing can really tell you how much either, it's a matter of the application and temerature. You dont need to primer the whole car either, just the spots that you did work too. Sealer is probably what you were thinking about peter.
There are a few ppl that paint on here. One is "brently" and TKRperformance is in school for it and I believe his car is coming along well.