I seem to have better luck when using a primer underneath, doesn't have to be thick, just good coverage. Then you can go several coats if needed with the top coat.
Probably the most important thing is to make sure the metal surface is very clean. Use some mineral spirits or accetone, or some degreaser to make sure that every bit of that box is clean and then don't touch it before you paint it. If you go down to bare metal, clean it prime and paint several good even coats, you'll be just fine.
The hammertone finish is a bit tricky, at least for me. That blue on my Huot is hammered, I just didn't do a good enough job of getting it thick enough to hammer. Too thick and it freakin runs

so it's a fine line. Also if you do a bunch of thin coats, it won't hammer either. The wire wheel gets the big areas fast, I used the sand paper and scraper for the inner corners and stuff. I didn't want to see layers of old paint under my new paint and figured if I am going to spend time feathering it, I might as well remove it.
It's not a five minute job, but it isn't really that bad. It was all the stinking drawers that took a lot of time.
I removed all the handles and drawer pulls and put em back on after painting the box. To me that was easier than taping off, but you have to judge when it might be just easier for you to tape a part off rather than remove it.
I guess I forgot a step in my description, if your box has drawers, you need to eyeball the tracks, runners and stuff and make sure they are all straight and aligned, but I guess that goes without saying. A lot of guys will get some green felt from the craft stores and use that on the bottom of the drawers after the paint is cured. I need to complete that step for several boxes.