If you run upgraded or aftermarket calipers, share the details and your rotor size.

I currently run R32 GTR Sumitomo front calipers, one of the calipers has been causing issues on and off for a while (banjo bolt thread is stuffed, so got it helicoiled but its more of a temporary fix) and run N16 hubs with 280mm rotors.
Ideally I'd like to run 300mm rotors for ease, in the future it would be nice to put some racing 4 pots on the front and 2 pots on the rear.

1) How hard is it fitting AP racing/Alcon/Wilwood calipers to N16 hubs? custom spacer/brackets needed? is it possible to run them on N15 hubs?
2) Anyone run 2-piece rotors in 4x100?
3) Or is it worth ordering 280mm 4x100 rotors directly from DBA (custom order)?