Hey, that's a pretty good analysis. A couple of pointers, though:
1. Pick the motor AFTER you figure out the battery. If you look at the specification of the 2820/10, you'll see that 12 cells is too much voltage: www.modelmotors.cz. If you've settled on 12 cells, you need the 2820/12.

2. Go with 1 Volt per NiCd/NiMH cell for your Watts calculations. It's a little conservative, but more realistic than 1.2 Volts per cell, especially under heavy loads. It's also a whole lot easier to calculate.

The application charts at www.modelmotors.cz will give you ideas on what props cause what current draws on the AXi motors. You can also interpolate how unlisted props will perform.