Re: Seeking advice on a frog and plant rack build
You should certainly seal all the wood - especially any engineered wood like plywood - with a waterproof coating. As a plant or viv shelf it's going to get wet and engineered wood does not react well to moisture. Paint will work fine. Polyurethane is another option if you'd still like to see the wood grain. Seal it now and it will extend the life of your shelf.
Is there a reason you extended the framing above the top shelf? Are you going to hang plants from the corner studs or add hanger bars?