For specs see:
Brake Wear Specs Use a micrometer or caliper to sample the discs in several places then avg. the readings.
For factory pads, the best price I could find at the time (early last year) was: Paragon Products:
http://www.********************************************************************.com/category_s/105.htm
So far as reusing the springs, it's OK at least once if they're in good shape - clean them up really good with a wire brush, especially the pins.
Also cosider flushing/bleeding the brakes, esp. if it's been more than 2 yrs., or if you don't know when it was last done.