I don't claim to be an expert painter, but I have painted a few cars, trailers, etc. with minimal equipment and decent results.
I do mostly hand sanding. Rust problems I scrape, wire brush, flap disc etc and then sand. Don't be afraid to start with very course grits and don't go past 400 so you have a good bite for the primer. Don't skimp on the primer quality but you don't need OEM Dupont, etc. I've used both Eastwood products and paint from PaintforCars.com and had good results.
I've done all my work recently with Harbor Freight guns ($10 on sale). They aren't ideal but they work. You should have a bigger orifice gun for primer but the HF only comes in 1.4 size and I've used it for everything with acceptable results. That said, I'm thinking of getting a better setup because my next project has a fiberglass body and I will need to use high build primer and will be spraying a metallic final coat. Whatever you do, don't be afraid to turn the pressure up and make sure your compressor has plenty of capacity. The specs for HVLP guns are at the spray head (which you can't measure) and not the air tank. You need plenty of pressure and you need to stay at 6 inches or so from the surface to avoid lots of orange peel.
Now the warning. Paint products are toxic. I use two stage systems with a clearcoat. These are isocyanate materials which require a fresh air breathing hood. I don't like painting anything with a spray gun without my fresh air system. Theoretically you can do single stage paints with only a breathing mask, but be careful. As for hardener, use whatever the paint supplier recommends.