Regarding the throttle linearity. You are correct, they are not linear. 50% of the throttle lever movemnet can end up providing 1005 of the power in many cases. Very little change in rpm takes place after the carb butterfly opens past the 65-70% point.

If you set up the travel adjust for the throttle servo at 100% you have a starting point. Next is to install the throttle linkage on the servo arm at the innermost hole. Install the linkage on the carb's throttle lever at the outer most hole. See where that leaves you and play with transmitter throttle curves if you feel the need for more linearity. Some people use exponential on throttle to achieve a similar "feel".

As for degree measurements, obtaining a couple of plastic protractors at a stationary, art, or school supply store is a simple and cheap way to obtain a workable tool. There are many types of angle finding tools that can be purchase for $10.00 or less at any home improvement supply store. That's cheapr than any of the "specialty" items obtained from hobby supply stores.