Hi!
I know this is a old thread but here goes...
The PBY Catalina by Kyosho is a very easy plane to fly off water if set up right (as any plane).
The first thing to remember is your own experience.Flying a twin is not as easy as flying a one engine airplane. So practice on other planes first before flying a twin.
One newbie mistake is over powering! This is one mistake that many new comers do as they think they can always throttle down. But this is not right! Overpowering and using larger / heavier engines often results in erratic flights that results in a crash.
Using a heavier engine/s that requiers more fuel, larger fuel tank/s and sturdier structure/s (which means more weight).
-See the evil down going spiral??
A much better way of powering a plane (not a racer or pattern plane though) is using "enough power"! Enough power means having experience from many many planes to what engine size to choose for what type of airplane. Knowledge you can only get from years /decades of flying and building.
Going back to the Kyosho Catalina. If you fly from sea level a suitable engine size is .15 glow engines like the OS FP .15 or LA. 15 plain bearing engines. Those are light and powerful enough engines and if propped right ( with APC 8x5 props) will fly the Catalina just fine with very scale like flights ( less than 1/4 throttle) and take off from water will be just as easy both in calm and a little windy conditions.
Above is some examples of planes to practice on before trying out a twin.