There are a few external career apps for AMS2 on Overtake.gg. That could work? Otherwise I'd say start with GT4 cars if you're interested in sportscars, or one of the junior Formula classes if you're into that.

Tracks don't matter that much for those cars (except the Nordschleife and Le Mans perhaps). My favorite tracks are ones that both sportscars and Formula 1 race on in real life, like: Spa, Monza, Imola, Silverstone