Anyone ever use this paint

http://www.equipmentcolor.com/

I own that site, so I can answer some of your questions. You can put either the enamel or the urethane over pretty much any automotive or industrial primer. In my opinion the best would be epoxy, urethane, or a direct to metal hybrid. If you just want to prime and shoot, then epoxy is the way to go. If you are doing bodywork or need to block the panel then a urethane or DTM primer would be the way to go. You can put the product over lacquer primer and it will work but the longevity of the primer is much less than the ones mentioned above.
With the urethane you MUST use an activator or it will not harden. The acrylic enamel does not require a hardner to dry. But you can use one if you like and it will enhance durability, gloss, cut & buff, and repairability.

Thanks,

Larry