You get so much XP from the special events that you don't need To do them more than once to advance a long way from level 17. There is no need to grind XP at level 17. You should have a decent variety of special events, licenses and races to choose from. It's only when you get into the 20s that you mig have to start thinking about grinding.
It is setup as near as I can tell so you can make it all the way up to Level 25 maybe 26 without having to grind at all you just have to gold every series and almost all of the challenges to get there. I just got to level 25 yesterday and have not had to grind at all. The only specials that I don't have golds on are the expert level AMG events since they were just unlocked and the final Loeb challenge event in the snow. I have all of the beginner-extreme series done with the exception of Formula GT and Dream Car Championship. I'm guessing that those will get me to or beyond level 26, then its on to the endurance.