what kind of solder wire should i use for my pickup? any general advise would be great too.
not really,

it depends on how you're gonna use it.

as long as you have 60/40 rosin core solder, and a gauge you're satisfied with, you should be fine
ok, the price diff is 1 dollar so for soldering a pickup should i use:

# 1 lb spool
# Sn60/Pb40
# 13 Guage
# 0.093" (2.36 mm) Diameter


# 1/2 lb spool
# Sn60/Pb40
# 21 Guage
# 0.032" (0.81 mm) Diameter
Well, I use a 60/40 spool (incidentally a 1lb spool) of rosin core solder, it's 0.062. I'm not a master of gauge, but I guess I'm using 14 gauge (2.36mm/0.093in is actually closer to 11 gauge...).

I guess you could always go for the lighter gauge (21). That way you'd be less likely to over-solder a joint.