Make sure you do what is necessary to keep water from running along the pushrods and ending up in the servos. When a servo gets water in it, it freaks out. Make sure that water cannot get to the receiver or the battery switch. Spray from the floats and the prop will get into places you wouldn't believe.

The small floats recommended will work fine. Get the step either over or up to 1/4" ahead of the CG, and make the floats about 30% of the wingspan apart. Take care to get the wing incidence about 1-2 degrees positive in relation to the tops of the floats. Make the struts tall enough that the prop isn't too close to the waterline.