@ThomasKoch try a good gameconfig like this one. But eventually you will run into an addon folder limit. Older game versions can run more addon folders then the newer game versions can.
Like a few have said you will want to combine your addon car folders into 1 big dlc file. Dont go over 3.95gb in size for the dlc.rpf file otherwise your game will not load. Under the tutorials page on the forums there is a guide on how to combine car addons.