No idea where to begin!

heres what ive done so far, pressure washed the whole car. front , to back, top to bottom. cleaned out the engine bay removed the front end panels and the doors.

Began to sand one fender panel down with the 3m paint and rust remover but after going through 4 just to do 1 panel I realized that those discs were maybe not the most cost effective way of going about it. Poisondart74 has been a great help, and he told me about these sanding discs that I plan to buy, I guess they go in an angled grinder?