You could power this plane with a cheap speed 400 direct drive or with a gear box. I powered a skimmer 400 with one (direct) and a 6.3X3 prop . Seven AE 600 cells. Worked great. As far as figuring it all out yourself do a search for" Motocalc" and download it free for 30 days. All the answers are in there.
Just cut off the nose to fit the motor and install the battery pack over the balance point. Move servos to aft of the battery pack and the Rx behind that. I use a loaded antenna inside the fuslage. Balance by moving battery pack. No need to ever add ballast to an electric plane!