What type of solder should I use to install pickups? And how many watts should the soldering iron be?
15w iron with 60/40 rosin core solder. The standards. It'll take a bit fo rthe iron to heat up, which is good so you don't fry your electronics.
Thanks, also to do with soldering, what is "Flux"
most solder nowadays has flux on or in the solder.
(The rosin core bit is the flux.)
Flux is something you would put on before you solder, it helps draw the solder into all the places you need it to go. The rosen core won't require it, more often its for things like plumbing joints and such.