Rick,

go here: http://www.mvvs.nl/prop-power-calculator.xls . Everything will be clear. This spreadsheet contains all the constants for popular propellers and corrects for altitude.

For the amount of "power" required, a short calculation from the electric plane world a good place to start. Basically it states that a plane needs 50 watts/pound to ROG and fly like a trainer, 60 W/lb for basic aerobatics, 70 W/lb for aggressive aerobatics, 80 W/lb for pylon racers, 100 W/lb for pattern, etc. One HP is 746 Watts.