RE: MUST use epoxy?
NO!!!!
eherm...unless you want your wings to fly apart in midair. The center part of the wing takes a whole ton of the flying stresses, and while wood glue is a decent bond, 30 minute epoxy is better. For all the high strenght areas, use epoxy otherwise it is likely th ebond wont last long.
epoxy is pretty cheap too, certainly cheaper than a new plane.
Hope this helps, and good luck!