1) Yes it will be subjected to more load due to the increased leverage over the OEM position like any other larger brake upgrades. I do not think this will be and issue due to the fact that others have mounted 13" + brake systems using oem sized m12 bolts and are to holding up. I would be more concerned about the aluminum hub than the bolt shearing; one reason I do not like the idea of drilling out the hub. OEM Z32 caliper bolt is a 10.9. I use a 12.9 because it was hard to find a 10.9 M12x1.5 for some odd reason. FYI, the R33 GTR Brembo setup are also 12.75" rotor with slightly different offset hat and use a m12x1.75mm pitch.
2) I'm not sure, I'd guess 13" but then you would need to find rotors with the same hub hat mounting offset as the Z33 Brembos.
