I can't answer all of them but I will what I can.
Bottom of fuselage? wood glue is ok. I would also put a fillet of wood glue along the seam.
Wing block? Epoxy
Leading edge? Yes alot of sanding, I use a razor plane to rough shape it then sand.
Use a sanding block on the wing joint to get a good flat finish, be carefull to keep any dihedral needed, test fit often as you sand.
Not sure about the tail feathers?