I like this idea a lot. How about making the league quite short. You could use the 4 or 5 most popular track/car combos that new players will probably come across. After all, if it is for beginners you will not have complaints about being unoriginal. For example i would replace AS cadet with AS club. Looking at LFS desktop, club has way higher track usage and as such would seem the better choice (although i am biased on that one).
For cars i would suggest the XFG for blackwood as an introduction that everyone is familiar with, then one SS, one GTR and one other popular class/model.
This should make it immediately accessible (as new players are bound to have experience with at least 1 of the cars or tracks). Even if they arent by playing through and practicing for the league they will gain a good grounding in all the most widely played areas of the game on which they can build. It should also make a great tool for learning and discussing racecraft. For example the penalty for crashing someone out may be starting a discussion thread on what went wrong, why and how to correct the problem rather than penalising points etc.
The benefit of keeping it to just a handful of races means there can be good accessibility as new players join the community, racers can move on and up without a long term commitment if they enjoy it and do well and it is not intimidating.
How will you define beginner though? Join date, laps, mileage, previous competitions?