1. New black Wiis & White wiis can't play disc backups. Impossible to know if it will have 4.3 but very unlikely.
2. This question doesn't really relate to softmodding, so I can't answer it.
3. Only a wii that does not have the d3-2 or d4 drive chip can play GC backups. GC games cannot yet be played from USB except VIA the WODE or SunDriver.
4. That is entirely up to you.