I agree with Mr. Huber about mounting the floats straight. Looking down from the top, it's important for them to be parallel to the airplane's centerline. No toe-in or toe-out, either. Looking from the side, if the top of the float is level, the wing should sit with a little up incidence.

The Aerostar has big stabilizer surfaces, and I have not seen it need more stab when floats are added. You MIGHT have the floats too far forward, tho'. THe step should be far enough back that when you put the plane on a table, it will rock forward onto the front part of the floats, and not rock back onto the transom of the floats. Generally, about a half-inch behind the balance point works. If you want to get technical, the step goes under the point that corresponds to 40% of the mean Aerodynamic chord, projected with the wing at zero incidence.

If the floats are too far forward, it hurts stability both in the air and on the water.