This config will allow you to bypass the limit on the number of cars added as an add-on, and traffic cars.
Gameconfig Installation path : Mods/Update/update.rpf/common/data/ back up your gameconfig then change whichever you want. Multiplayer values meaning: Like 4x traffic means 4 times more vehicles spawn only around you(Ambient not all map). Multiplayer values meaning: Like 4x traffic 4x peds means 4 times more vehicles and peds spawn only around you(Ambient not all map).
About traffic density; if you choose the gta base traffic its same gta 5 traffic but you can add how many cars you want.Start with 1x taffic more vehicles on road choose whichever you want for your taste.