go to heads up rc. read motors. much easier now that they have them listed according to size.
take the projected all up weight of the model, use this as a base line. pick a motor that gives you enough prop clearance and has at minimum a 1:1 power to weight ratio. heads up posts actual thrust from motor testing. 5lb model, 5 ounces of thrust. another good number to shoot.for is 100 watts or more per pound.
my ultra stick flies nice and even has some verticle on 350 watts. with battery, it weighs about 4 lbs (4000 mah 3 cell). same setup on 4 cells, 830ish watts(same prop) 3000 mah battery, unlimited verticle till you cant see it.
some would argue 350 watts isn't enough to fly the plane and would be unhappy with it. others would say 830 watts is way too much. but both will fly the plane.
using this as a guide, it WILL fly the plane. I like to over motor and then under prop/throttle back.