I think Larry is talking about grinding off the screws. For the rust, I would not use a wire cup brush and angle grider. The RPM is too high and the wire wheel will grab that thin steel edges and bend the snot out of it. Use a wire wheel on a drill where you can control the RPM's. Then you want to go after it with some sand paper to clean it up and smooth it out before treating and painting.
If you want to grind screws off, use a grinding disk for the angle grinder.. But, I think the screws are actually stainless and will probably be easy to remove normally.