No idea where to begin!

Don't sand the whole car with 36. 320 on a D/A (dual action) sander or with a sanding block would work well for the whole car. A D/A would be faster. Remove all the trim and emblems before you sand. That roof pillar rust is probably worse than it looks. I think you will be happier in the long run removing the glass and getting rid of ALL the rust on that pillar. It looks to me like it has infiltrated the glass sealing area as well. Take a pick hammer to that floor pan rust. I can see in the pics that it is also worse than it looks. Whenever you find rust, you find more rust. The ONLY way to stop/get rid of rust is to cut it out and replace with solid metal. Always cut past the rust until you are on solid metal. That door lock hole can be repaired either by hammer and dolly work, or possibly cutting out and welding in a new piece from a donor door. Your car needs a lot of work, but it is a good solid starting point. I have brought much worse back to life, and I'm just a hobbyist myself. Everything I've learned, I've learned on the fly. YOU CAN DO IT!!! Good luck. We're here for ya!!