there was a kalmbach book called "scenery tips and techniques" that covered water pretty well. I am not sure if it is still in print. Coloration is personal choice and expect it to take experimentation, and plenty of mixing. Study real water objectiely. People have a tendancy to want to make water "blue" and grass "green" when in fact neither may be correct. If I were doing it, I would first put down something over the plywood to help smooth the grain. Maybe a thin piece of masonite or linoleum. Or you could try joint compound. Next, I would put down several coats of white, flat latex paint - maybe with a roller to hide brush marks. Artist's gesso could also be used for this. For painting the water, I would use artist tube acrylic paints. But then again, I paint as a hobby and this is natural to me. Small bottles of craft paint would also work well - they are cheap and come in many colors. I would buy many colors of blues, browns, tans, greens, and experiment. I think a 1" brush would probably work best - and take extra care to blend the colors well along the shore. natural waterways don't often have abrupt changes in color, except when the sediment load changes do to river input. For the gloss - I am sure someone at an art supply store could point you to a high-build gloss medium that you could kinda "stipple" on to represennt waves. For really choppy water, you could stipple the waves, drybrush the crests lightly with white, and then apply more gloss.
kevin