Why the etching primer? I think epoxy will take care of it.

Sandblasting media won't get down in the seams. I would get 80 grit and sand the seams to bare metal, or put clay on the ends of the 4 joints and pour a little evaporust down in each seam to get all the rust out before blasting. After blasting expect to have to dig out stuck media particles.

Get a small paint brush from an art store and paint primer down in the seams. Then before you paint brush a little paint down in the seams too. The first place they will rust is the seams so if you get those clean and sealed up your better off.

2 part filler or JB weld any ugly gouge marks in the wheels.

To get the paint smooth sand the orange peel out of the epoxy primer with 600 grit before painting that way your not stacking orange peel on orange peel. It does make a difference if you want them super nice. You can paint over the epoxy days later so no need to worry about that part.

Tack rag before painting.