#2
Poly wire is the standard crap that comes in most guitars.
Braided metal wire is shielded and is used in Gibsons and hollowbodies, where you want to use shielded wire to reduce hum.
Cloth wiring sounds cool and is very easy to work with. And it looks good.
Pickup wires are for extending the leads of pickups if you've cut the leads too many times or want to try a bridge pickup in the neck etc. Some pickups have two conductors, some have four, hence the option.

good places to find guitar parts:
stewmac
allparts
mojotone
guitarfetish
google