Hi Timdog. Welcome to the site and to the forums. Liam is right on the money about using a layer of glass over the plywood. Just a coat of epoxy will crack over time, which will allow water vapor into the wood and eventually rot it out, with the result of a soft floor....even with marine Plywood.
If it were me and I wanted to avoid using glass on the underside, instead of epoxy I would use a Urethane type of coating such as Rhino Lining or U-Pol. That will at least flex and not crack, thereby keeping the water out. But there's an additional benefit from using glass which you don't get with Epoxy or Urethane... Structural strength. The additional layer of glass under the floor makes it stiffer. You never know when you're going to have something heavy fall on the deck, or a heavy person jump down from the dock, and the stronger it is, the better it will withstand the force of the fall.
As to the nameplate, there are several posts on here, some with pictures, of the actual data on the plate, as well as people/companies that make replacements. Just click on the search button and enter in what you're looking for to find them.
And again, welcome aboard. Hope to see pictures of the boat and it's repairs. We love boat porn here.