Refinishing metal mail sorter

I have a metal (mail?) sorter like in the 1st pic that I want to paint black. I have experience with furniture refinishing, but not with refinishing metal and I'm just looking for some advice. Should I grind it down before painting? It has some rust and I wouldn't mind if some rust showed to give it an edgy rustic look, but if that sounds dumb and I should grind it all down, I'm open to suggestion. Also, what type of paint? I know I wouldn't want to use a latex wall paint, but what about enamel or chalk? Thanks