$32.99 each.
http://www.blackhawk.com/product/Sportster-SERPA-Holster,1146,1410.htm
Contact Glock and they will send you a manual for free. You can also download one from the Glock webiste.
Follow the instructions in the owner's manaul. If you don't have one, call Glock.
Impossible to answer without more information. Both are fine weapons.
100-400 USD depending on condition.
Depends on the load and what you are comparing it to.