I didn't found any gameconfig that would let me play the game with more than 1 add-on vehicle, so I decided to modify it to actually be able to play the game.
So far so good, I've got around 20 add-ons cars + LA Roads, Forests of Chiliad YMAP, Added Aesthetic Trees, Beta Vegetation & Props.

Had no issues so far, using this from 4th september, when scripthook v got updated.
0.1v2:
Added second option gameconfig. In the main .rar is the new one, also in this .rar is another .rar (lol) and it's also another custom gameconfig based on the 0.1 (initial release).
0.1:
-> Initial Release
This fixed me 3 problems:
-> not spawning some add-ons cars;
-> infinit loading screen;
-> crash during loading screen.

Install here: mods/update/update.rpf/common/data

Link directly to gameconfig, no winrar needed:
https://mega.nz/#!5qJhSRRC!d_Zf8Yt2TxIAR2mSf5R12GJB6SzOJ1NkSdYKGSroFFY