Hi I really like the feeling of Free Roam and just like driving around and it would be lots of fun to have other vehicles driving around too - but can i ask- Is it possible to have CPU/ AI vehicles ingame as well?
Yes... But you have to manually spawn them. Just spawn a new car of selection, bring the AI app up and set it to random, then it will do its own thing.
To build on what Cheekqo said, there's a more complex way to do it if you want individual cars to have different behaviors at the same time. First, add the AI app to your UI. It'll be on the bottom left of your HUD by default, like so. By default, it'll be set to Disabled, which means you can drive the car as normal. Next, switch to the car you want to "program" and click the AI mode bar. Switch it to "Random", which will only work if the cars are on a road, obviously. The car will now drive itself. There you go! You can now choose which cars drive themselves, which cars you can drive, and which cars flee and chase each other, which I can make a guide for if requested.