[Michael Pierce]

Hi everyone
Just signed up, and this looks to be a fantastic feature. I could not find if you need all DLC to participate in races. Is that the case or is that class specific?

depends on the series.  You will need all of the cars for that series to race it.  If you go into the app inside of AC it will tell you if you have some missing as you try sign up i think.  (it wont sign you up if you dont have it, IIRC)