nice that you are interested in setting up a GPL league.
I am admin of http://www.gplracer.eu
and you are welcome to have a look around our site and forum. You might get some ideas there.
As the number of people who race GPL online in leagues has declined over the years, the remaining drivers are usually already in the small number of leagues that have survived.
Therefore I would first check if there is an active GPL league in your timezone (where do you come from?).
You can get a good overview of active leagues at the GPLrank site: http://gpllinks.org/
Because it might be difficult to set up an additional league, if there is already a well established one in your timezone.
Edited by Stefan Roess, Dec 01 2011 - 04:48 AM.