1. Something to heat the bearings and synchro sleeves.
2. Depends on what it needs when you get inside. Gears can get pricey.
3. Other than being a transmission, about the only thing similar is setting up the ring and pinion.
4. If you can already rebuild a transmission, a G50 is similar to any other modern transmission.
https://forums.pelicanparts.com/porsche-911-technical-forum/1157509-guy-his-garage-attempts-rebuild-g50.html