the wire coming out of the bridge will be a ground, or at least it should be.
using 500k pots will be fine for the singles, but you could use 250's if you wanted.fender used 1meg pots in the teles in the sixties and they sound just fine so like i said 500's should be good.
as far as i know BKP base their HSS sets on a 5 way switch that gives you the screw coil of the humbucker and middle position single in parallel, are you going to be using BKP's?
also, i know you said you don't want to split the coils but you may find that a two way on/on switch would be perfect as it could give you hum/north single split which means you could easily switch the humbucker to the north coil for position two. its not as inconvenient as you might think using a two way coil split, its much simpler for quick switching than the three way ones.
after saying that, i would still hope that phillking will save the day.(He knows all things)
PHILLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLL!!!!