Preparing for rust removal

I needed to look at a few things from my car to ask questions about before I start working on them. These bolts for example. I need to remove 1 door hinge but I don't know what these bolts dig in to. If I remove them, will a nut drop behind it? Will I ever be able to reach?

Apparently they are bolted into the frame, so no nuts, great!

I also did a little rust inventory. After I remove the rust under one of the hinges I'll do the rust around my rear lights.

And other little things like this...