RE: Rebuild....but different
1. yes
2. spiral stability, it will tend to tighten bank in turns unless you make the fin bigger. You will lose any yaw/roll coupling which may be a good thing, depending on what you want
3. nah, doesn't matter. Regardless, the wing has to go through the same angle of attack change for inverted flight. It just won't be as snappy inverted, if at all.
4. yep, if you take the dihedral out, making the fin taller/larger is a good idea.
moving the cg back a little will make the controls more sensitive and help the inverted flight trim. I would add surface area to the tailfeathers, so as to maintain stability.