Although I admire your desire to do this yourself, I think you need to learn a LOT before you proceed. I base this off of your quoted question and what you have said. There are LOTS of videos available on how to paint your own car.
Let me just say that surface prep is absolutely essential. The following is what I did. There are other ways to do it, but there are no shortcuts.
When I painted my 69 Barracuda, I stripped the body down to bare metal. Then I sprayed epoxy primer on it all. Then I did the bondo work, then I sprayed on 3 coats of high build polyester primer, then I applied guide coat, then I block sanded with Dura Blocks using 220 and 320 until most of the primer was gone and the bad spots were revealed. The darker guide coat will still be in any low place, so you can easily see where you need to do more work. Then I filled all those low/uneven places with high quality spot putty and blocked with 180, 220 and 320. Then I sprayed on 3 coats of high build polyester primer again, applied guide coat and blocked with 220 and 320 until all flaws had disappeared. Then I blocked with 400 grit dry, then 320 wet followed by 400 and 600 wet. Then I painted. I spent at least 80 - 100 hours priming and block sanding my car. There are no shortcuts. You CAN paint over existing paint (although I would not do it). You need to block the old paint with 80, 120, 220 and 320 to get rid of the problems you are talking about and then apply 2 or 3 coats (I'd go with 3) of I high build polyester primer then block it as mentioned above. Failure to spend an appropriate amount of tome on prep will absolutely show up in the final result.
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