@ nvooght- have a read of Vader's sticky at the top of this forum called something like "GP3 FAQ & Installation Guide". i think most of your questions will be answered there. it offers links to best downloads and explanations of how to install them as well as lots of other info.
once you're up and running, i'd also recommend having a look through the old downloads section on this site- click the link on the main page. there's so much awesome stuff, carsets, carshapes, tracks from all over the world etc etc. enjoy!!