I have a standard answer for anybody wanting to start float flying: Take your favorite sport plane and add floats.  You'll be flying a familiar plane and your learning curve will be MANY slope-points ahead of where it would be if you start with a new plane/new environment.  Most any RC sport plane has adequate control surfaces to handle well with floats.  AND (unlikely) if you find that floaty flying is not your bag, then all you are out is the dinero for a set of floats and not a whole new airplane. 

Dittos on the Sig Kadet Senior as being the GREATEST floatplane.  I have one tricked out with a flat, bolt-on wing, Ailerons and flaps, and the significant features modified to look like a CUB.  Mine has PlaneFun flots (42") and a HeadsUp Sport 60 Electric, on 4S 4200 battery pack running thru a 100A ESC.  Vertical Performance! YeeHah!  Smaller Kadet models work well, too. 

My other standard advice is to use foam-core floats.  They are lighter, which affects the airplane's handling less.  They are more durable because they can't leak and sink.  They can leak-but they are repairable.  Plane Fun Floats, and Seaplane Supply are my top choices.