Good Morning, ringing in here just to say I absolutely concur with just about everything 52Larry52 has posted, indeed lots of good information there. About the only thing I differ in and that's just me is I hate box mufflers (pitts) and avoid them for stock ones on the that size airplane even if the engine mount has to be rotated to an odd positon or a tunnel cut in the firewall for a stock muffler, agine that's just me
If you are new to float planes I just want to add one point about CG. Now since this is the size and may be the type of float plane where it is desired to fly both on wheels and floats. The very best way to acheve easy change outs between floats and wheels is to set up the airplane on wheels first and yes even fly it and balancing it at what ever position it flys best. Yes always balance with empty tank. Now mark this CG, This will be the exact same CG that you want the airplane to balance at when floats are installed.
In the majority of that type of airplane on twin floats when you install the floats from wheels it will normally come in tail heavy or that CG position has moved aft from where it is at when the wheels are installed. In this case the trick is to not go back to the airframe and start moving stuff or adding weight to get the CG back to that same spot when it was on wheels. The reason is if you do that then every time you just want make a changeover your will have to do it all over agine i.e. adding/removing weight or moving stuff.
The solution is to simply add weight (yes and this is one of the rare times I suggest using lead) to the floats and normally right up in the tip of the bows. I just cut in a little hole in the top deck of the bow and drop in the lead then some epoxy or ca. and cover over with a patch of monocoat. Use enough lead to move the CG back forward to where the airplane flys best when on wheels. In this way change outs can be done very quickly and you actually will never have to balance agine.