Vault 4 is hidden in the Wasteland; you'll need to search around to find it.
The security robots will attack anyone that doesn't have an apartment and moves onto its tile. Since the only exit once you're at the apartments tends to lead straight past the robots, you'd be well advised to steer clear until you're confident in your abilities to run like a sissy girl.
Rent: $10000 down payment and $500 a month
Security: Three Crazy fuckin' robots with bad tempers, general obscurity, built-in VoxGuard Bronze.