The best way to make it look like a city is to use the Junk Yard Dog AI, have locations all around the city, so when they try to exit they get ordered back to a location where the AI Junk Yard Dog is constantly being run.

Where is that script i've never seen that.

Its a trigger action: "AI script"
Then choose the type of ai and find yunkyard dog in the list.

Its specific name is: Set Unit Order to Junk Yard Dog

How do i make it so that two computers are hostile towards eachother? should i have them in different forces or untoggle the allied option when in the same force?

There's an action to "set alliance status".
Lets say they are P7 & P8:

P7, P8
Conditions:
Always
Action:
Set P7 to enemy
Set P8 to enemy

Note that I put both actions into 1 trigger owned by both players.
It works because you cant unally yourself. (Though you can unvision yourself)

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