Same problem here, but Happy to have a problem like this.
I'm new un Assetto Corsa and I spend more than six months collecting Cars, tracks, skins, apps and all this increíble stuff moders made for the Game. By now, I have more than 200 tracks, over 1600 Cars and many days I felt like you, don't know what Drive or where, but I'm in love of everything that have four tyres and wanna go fast, so always found the perfect car for the perfect moment.
Now I'm training to Race the 24H of LeMans 1998/1999 and Drive every car trying to find the perfect for me, by now, the URD Mercedes CLR is my favourite until I try the RSS pack. For me Assetto IS a Game for a decade, so no need to be hurry.
If you want an advice, erase every car and every track and instale only that you want to Drive in this moment, a real pleasure, believe me.