For steel doors and decorartions I like to use a Rustoleum red oxide primer and a Rustoleum, Sherwin-Williams Industrial, or similar oil based high gloss paint.

Prep is the key when dealing with rust. It can hide in the smallest of pores and crags even though you can't see it with your eyes. There are some acids and caustic solutions that can used on the steel after the sanding to help remove the impurities.

1. Wire brush the rusted areas.
2. Sand the rusted areas to feather edge the surrounding paint. Start with 100 grit and progress to 120 grit to finish sanding. Then sand the entire door surface with 180 grit, including all 4 edges.Remove sanding dust.
3. Wash the door with a degreaser. A strong solution of Dirtex will work. Rinse and dry with a towel.
4, Apply a rust inhibiting primer with a 4" nap roller and back brush with appropriate brush. Be sure to prime the entire door surface, including all four edges. Do not use a foam roller. The nap will work the primer into the pores and prevent future rust.
5. Choose a quality exterior acrylic enamel. Apply two coats with a 1/4" nap roller cover (Wooster makes the best) followed by back brushing to level the stipple. A light touch with the brush is all that is needed to level the paint.

Thank you both so much for your advice. Hopefully, the weather will be decent and I'll get it done this weekend.