Having flown floats onto still lakes I can say the most important thing is control.
You do not approach at minimum speed as this can lead to loss of control and high rates of descent. The important factors are body angle and minimal rate of descent at touch down. Some float conversions have the final stage of flap locked out for that reason. In a powered float situation you come down to a reasonable height above the water set an appropriate attitude and power to gently settle onto the surface, as soon as you touch down, cut power, and pull back, the hydrodynamic drag will suck you onto the water so you won't balloon. If you approach too slow you risk developing a high rate of descent, for a land plane this might only result in a heavy landing or bounce, in a seaplane it will be terminal and you'll end up inverted.
The reason I suggested a faster approach speed without power is to maintain control during the flare and touchdown, the idea is to be able to transition to the correct attitude nose high and allow it to touch down at minimal rate of descent. This in no way means dive bombing the sea in a nose dive, it just means carrying a few extra knots above normal landing speed.
The Perth ditching really demonstrated the importance of control during the touch down, she maintained back pressure, so however unlikely it was, the aircraft skiid on the water and resisted biting nose first.
You have to remember as well the sea is not a static target, it's moving and pulsing, so there can be a lot of visual illusions as you approach.