RE: Where should the step be?
Bob has probably forgotten more about models than I ever knew, but I will disagree with him about the location of the step-with a small caveat.
Having the step under 40% of the mean Aerodynamic chord has always worked well for me. All my references put the step behind the CG, And it's easy to see that it would be a little more stable on the takeoff run with the contact patch behind the CG. I have never even had to add balance weights when adding floats.
Caveat: As long as it's not too far forward, Bob's method will probably work,. It has worked for Bob, and that's why Bob swears by it. It's like taildragger landing gear. From a stability standpoint, it's suicidal,but lots of airplanes have survived it. You'll notice videos of Spitfires taking off from nice slippery grass next to the grippy paved runway.......