BMatthews

You're going to pick up a puck on the fly similar to picking up a load of water? You'll need to build the catching setup to handle an impact consistent with a full swung hammer blow

For water proofing any of the usual polyurethane varnishs or similar film finishes will do fine. The next trick is to seal all openings. Tube in tube pushrods form a good enough water resistant seal that they work fine. The wing to fuselage joint needs to either be sealed fully with weather stripping or you need to provide an inner cover that is water tight. Same with any other systems access hatches.

I hope you're going to enlist the services of a suitable pilot. These things seldom fly just like the simulators that you may be using to practice. In particular watch your weight. Each size of model has an optimum wing loading that you want to keep within or the model becomes more difficult to fly well in various conditions.

The good news that I see in your plan is that you're at least starting out with a known design that has all the structural engineering done for you. Good move on that part.