Mmm, not too sure. Depends on the class you're racing.
Rookie class is relatively easy and low on costs.
It only runs 2 tracks on the road series (Mazda MX-5), Laguna Seca and Lime Rock Park.
These are all free with your initial subscription.
Once you get a feel for the driving model, all you have to do is practice a couple hours 'til your driving becomes reasonably consistent and I'd say you're pretty good to jump into a race.
To be competitive, it's all about staying on the track with speed coupled with lap consistency... no diving into corner 1 like a maniac as you see in most other racers.

For the seasons, it's really up to you how much you put in... as only your top few races actually count toward your final spot on the season ladder. So you're not really required to race every waking second of your free time to actually count, which is nice.
As for GTR Evo, hit me up on Steam if you ever feel like doing some laps.
I haven't played in forever, but the WTCC cars are good all-rounders for beginners and experienced alike.
Here's my Steam profile link:
http://steamcommunity.com/id/supervillainoutcast