#1
what (material) do i need when changing pups?
do i need to change the pots as well? how do i know?
help please!
#2
When changing pickups you're definitely going to need a screw driver, a decent soldering iron and solder and pickups

You shouldn't need to change pots, unless you're changing from passive to active.
#3
i'd like to know what type of solders are good. do you "grade" the solders? like high quality solder or low resistance solders?
#4
No, just some thin rosin core solder would be fine. The rosin core contains flux, witch cleans the metal and allows solder to stick to it. Pretty much anything but plumbers solder, that contains corrosive acids and really wont work.

But for soldering irons dont get a really cheap one, something like a 25w would be fantastic.