1 & 2: Cant comment much other than to say I originally bought a bosch for the GTR, but didnt like the way it didnt fit the cradle or use the fuel pick up sock, so i swapped it for a $200 more expensive sard.
3. Skylines have an earth switching pump controller. I think ppl get scared because they see 12v at idle, and dont realise this is because the controller has used a soft earth to drop the voltage. The controller switches the full 14+V when required. IMO the only reason to go for the direct earth is because the controllers can fail (mine did).
4. Most ppl who change fuel reg's waste their money. Typically its a hack to get a little bit more flow out of your injectors. Pretty sure the stock 370cc injectors are ok for 200kws but thats about their limit.