rookie paint job

I'm going through the same thing right now. 70 Duster, that I bought new, got divorced, gave to wife, she had a cheap paint job done, just because of 1 fender dented. Re-married her, got the car back; so I know the history of it.
I'm using a palm sander with 100 grit, to cut off the 2nd coat and the primer; leaving the factory coat(it stuck, didn't it)
As far as bare metal, go to local auto paint store and get material, or go to local hardware and buy ospho (phosphoric acid) and treat bare metal. before any bondo.
Then prime/seal with Dupont. From the local store. Those people sell to pro's, they know what you need.