Gamers Crib is running one public server. But I have never driven there so can't say if you can get proper online racing practice there.
If you feel confident enough that you can complete a 15 min qualy + 30 min race with a grid of 20+ cars with gentleman like maneuvers without it turning in to a crashfest then I'm sure you are welcome to join in for the league. It's a pretty laid back and there are multitude of different skill levels on the grid at the same time.
For some reason there is no sign-up thread for the current season (4) but if you post about it on some of the threads here I'm sure you'll get in.