Boldaslove ...
It's 50mm spacing for Gibson type guitars and 52 mm spacing for Fender type guitars. It's just to ensure the indvividual strings pass over the centre of the pole pieces as they leave the bridge saddles.
As for conductor types, the 4 conductor wired pickups would enable you to later buy a switch to put the pickups out of phase with each other, or split one/both into single coils etc. This can be done without cosmetic alteration by getting a tone pot with built in switch from BKP and then when you pull up the tone pot, the switch does the trick with the pickup. Tim can/does send you the wiring schematics in either case.
Unless you want 'special effects' - the standard 2 conductor wiring looks more 'traditional' i.e one thick wire wrapped in braid.
As I said, Tim is always helpful.
P.S.
Phil king ,
Thanks for the link mate !
Regards,
Derek.