I am actually been in the process of doing body work also. I have used Bondo allot over the years and learned a couple things that really help.
1. When filling in dents, drill little holes in the crevices to give the bondo something grab onto.
2. Be sure to sand to bare metal before applying Bondo on the area you want to cover.
3. Clean, clean, clean, and then clean the area again before applying.
3. Buy some glazing putty it will be your best friend, apply on top of the bondo after sanding, the glazing putty is thinner then bondo and will fill any imperfections left after sanding. Once dry sand that smooth.
3. Apply high build primer liberally to make sure you cover any left over imperfections. After the first couple coats, you will still see the bondo underneath keep spraying and sanding until you can’t see, or feel the bondo.
4. Be patient, don’t slack on the sanding. Bondo can be your best friend or worst enemy. It can cover imperfections if done right, or make them worse if not done right.
5. make sure you have about 2-3 times the amount that you actually think you will need. You will waste alot of it.
All in all take your time, and rejoice to the fact that your making your car a little ricer