It is not that complex if only it were easy to measure mechanical stuff like horsepower or torque. It would also be very useful if we could accurately measure the power it takes to turn a given prop at a given rpm. Bob Boucher has a prop chart based on theoretical calculations as well as some "factoring" as a result of testing real props. I feel it is a little on the high side (more power than actual) but it is better than nothing. So if you know an APC 15x10 at 9000 rpm is what you want you can find out how much power that requires from his chart. You can then assume an efficiency and calculate the power needed from the electric motor. That part is easy.

I did excactly what you suggest by copying Tony F's setup and it has worked flawlessly for over a year. I wanted something I felt was better than a glow power system and liked what I saw in his plane. However, the beauty of electric is you can select a motor to turn the prop you want at the rpm you want. The only problem is cost and weight.