2 cents from the sign painter...

I prefer to paint between coats of a finish. I believe in your case I would paint over the epoxy and follow with a UV protective varnish.

I HIGHLY recommend using One Shot brand paints. These are professional lettering enamels. They are very opaque and flow beautifully. They also tend to stay where you leave them.

One warning...One shot is lead based. Wear rubber gloves if you are one to get paint on your skin. Don't allow kids and pets near them until they have been overcoated.

Geoff Davis