RE: breaking in a new motor
I'm going to flip that a little. Heat is a good thing when managed correctly. A 10 pitch prop is both more load and more speed. The 8 pitch will fly a little slower but with more pull. You're call here.
How you manage the throttle and cooling will determine what the engine can and will do. If you just slap a prop on and go for the gusto the engine will be rather short lived and never develop the power it could have. If you take things easy for a couple gallons of gas, never getting the engine too hot or letting it run to cool or cool too fast, things will be a lot better. Personally I'd run a 22 or 23-8 on the engine from the beginning but I would also tune the engine correctly and assure good heat management and cycling.
None of you break in an engine like I do because it's labor intensive and takes a lot of time. At least an hour and half with a very good cooling supply and live temp monitoring. However, all of you can perform a good break in if you do it in managed stages. Idle for 30 seconds, then 1/4 throttle for 15 or 20 seconds, then repeat the idle. Do that repeatedly while incrementally increasing the rpm a little at a time and things seat and cycle well. Hard to do that process in the air though. For an air break in just avoid full power for the first tank of gas, and don't do any extended uplines or 3d. Gentle aerobatics for two tanks minimum. No 3d for at least 4 tanks of gas. Once you go to full power don't hold it there. Short periods of high throttle with cool down periods in between the power runs. Do that for a gallon at least.