I don't agree with that at all.
First, to answer the original question, the float need to be long enough to have minimum 10% of their length, up to 15%, ahead of the prop. I usually measure from the prop to the CG and multiply by 2.5 to get the float length.

As for step placement, I did some systematic tests a number of years ago and wrote it up in a magazine article in March 1998. here are my findings.

Aft Step Position
We usually recommend placing the step just aft of the CG on models (floats or flying boat hull). On the full size Catalina the step position is a long way aft of the CG, and one supposes they did it for good reasons. Adrian Rowe-Evans wrote about building a nine foot span model of the Catalina in the British Waterplane Association newsletter, and noted that to get it airborne he had to put a step in the hull just aft of the CG; the scale step 6" aft of the model CG wouldn't do. He could get the model planing, but not airborne. I decided to investigate the effect of an aft step on a model floatplane.
I took my trusty 76" span PeTe floatplane and extended the step with 6" of blue foam to about 7" behind the CG. It will be impossible to take off like this so I took some tools along. The idea was to cut off the added foam, bit by bit, until the model would take off. I would then find out how critical the step position is.
First time, with a gentle breeze rippling the water, I opened the throttle and off it went across the water, and up onto the step. I teased on some up elevator to get the feel, and up it went. It took off. "Don't you read the books, you stupid plane?" Oh, Well! I flew it around for a while and of course it still did all the loops, bunts and rolls it could do before. What about touch and go landings? Yes, them too.
The modification had increased the step depth to 0.83" and the sternpost angle effectively increased from 5 degrees to 8 degrees, which may be significant. I added more blue foam to restore the original step and angle, and took it back on a glassy calm, still day. Initially it seemed to be sitting a little more nose down, and throwing up more water than usual, perhaps because of the extra buoyancy behind the step. It did eventually get up on the step and, accelerating well, the model set off across the smooth water, planing at high speed as I pulled more and more up elevator. I hit full up, then up it went. It STILL flies! Granted it needed full up and full power, but it took off and flew.
However, landing was a little bit fast, and on touching down the model suddenly plunged its nose forward into the water. It has never done THAT before. It appeared that the new surface area just ahead of the step, which is now a long way behind the CG, hit the water first and gave it a nose down pitch which was enough to drive the floats nose first into the water, and the model came to a very abrupt halt. Further landings were flared out a bit more and were more normal, though not quite so easy as with the standard step position.
I then started tearing off the blue foam, a bit at a time, flying the model after each change, and the original delightful handling gradually returned. I proved that step position is not critical, but if the step is too far behind the CG the model may sit more nose down and throw up more spray. It may not be as directionally stable when planing. It may be more reluctant to rotate and leave the water surface. And it may be more difficult to land.