1) I take it you decided to make the neck?
2) I can cut the groove, since we used a small router.
3) Yes. Now that I have Inet, I can look st some SG bodies. I am going to guess it is similar to the LP, where a small hole is drilled to connect the closest bridge (tailpiece really - strings act as the conduit to bridge and tuners.)
4) Depends. Some of the templates we built used bearing guides - the bearing is at the bottom of the bit and is flush cutting. Some other templates required a normal bit and used some required a router bushing.
Rockler Router Guide Bushing Kit - Rockler Woodworking Tools Templates needed to be made bigger for the bushing. Size is dependent on bushing used. 1/8" 1/16"...
5) Not much.