I'm still a bit confused by all of the licensing and cars and stuff. Is there a definitive list of licenses, which cars/tracks are available at each level, and which cars/tracks you have to buy?
The best bit is to go to this page:
http://members.iracing.com/membersite/member/Series.do
That lists all series, sorted by class (pressing the class icon at the top will jump to that class, likewise road/oval/multiclass will filter the results)
For a particular series press the + icon to expand that which will give the schedule on the left, content required on the right, any content you don't have will have the price by it.
The free cars are:
Legends and Streetstock on the ovals
Mazda-MX5, Solstice and SRF on the roads
Tracks aren't restricted by class but the free ones are (off the top of my head):
Summit Point, Lime Rock Park, Laguna Seca, Lowes/Charlotte Motor Speedway, South Boston, Lanier and I believe Oxford Plains as well.
Probably missed a couple but once you've got an item whether free or not it just doesn't list a price, so can't tell as I've got it all
EDIT: Didn't realise you didn't know the licence progression, what CatMangler said is pretty much correct, one thing though is that your SR isn't automatically reduced to 2.5 when promoted, it is effectively just calculated on the new 'rules' for the new licence (each time you go up a licence more corners are looked at to create your SR, and the criteria of 'corners per incident' also gets harsher) usually that ends up being around a 1.0 drop for every licence level but that varies quite a bit.
Have you read the sporting code yet? might be worth a go as I'm fairly sure it covers bits like this, it's in the reference section of the website...