#1
Im building my first guitar and cannot decide between a humbucker or single coil pickups

i mainly play blues with small amounts of country influences
#3
Why not have one of each or possibly one humbucker and 2 different single coils?
#4
P90s for da real blues. Or hums with series/single/parallel switching. Something like an SD JB works well for this, I'm doing it with SD Jazz on a very dark-sounding guitar.

If you are into tinkering, another one to try is a 12-screw-pole humbucker and remove half the poles to give a dummy or Z-coil type pickup. I've recently done this with a 10K ohm humbucker, and I'm pleased with the result
#5
It might be best to go with an HSS configuration. You might want to look into coil-splitting and push-pull pots too.
#6
I would put a bucker in the bridge and a sc in the neck! Coil splitting, like others have said, is indeed a good idea. I have a telecaster that has two Duncan humbuckers in it (2nd hand, so I'm not sure which exact model) and both of them are split and the single coil positions still sound pretty good to me.
And I'm not saying you should build a tele, but to me this just screams tele!
Call me Kerouac