No GTL mods need the disc. You may be thinking of the HistorX mod for rFactor, which requires a copy of GTL to install. However, it supports both the DVD and digital version, so you're far better off going for the digital version direct from SimBin.
A digital version of GTR 2 was planned, but got delayed because SimBin was too busy doing other things. (GTR 3 and final Race 07 expansions) It might be back in the works now, I don't know. However, from the info on RR it looks like all the Ferrari's are being cut from the game. Better off getting the DVD version if you can find it anywhere. I'm after a copy myself, but not for the stupid prices I'm seeing at the moment. (£50 in some cases!)
The GTL club is probably one of the best places to start racing online on PC. Extremely friendly community and a nice relaxed atmosphere.