DANGER Will Robinson! Seek professional help. And a flying instructor. Seriously, on the water will make learning 2X harder, at least. You nose over a trainer on the land and you shrug it off. You nose over a plane on the water and, if you get to it while it is still afloat, it's two days drying out and hoping the receiver survives the dunking.

I'd definately recommend the .46 in this case. The .40 LA is a cabable enough engine, but the .46 on the Avistar (a better performer than most trainers), especially one destined to carry the added weight of floats, is a good combination. I have used a Thunder Tiger Pro-46 for several years and it has been a good engine.