Ok. Was gunna post this IC but I am ridiculously tired and shall be asleep soon. 

Buses are heavily dependent on computers to co-ordinate their various systems, the data from which will have been wiped by The Blackout. What this means is that even if the lighting, the pneumatic suspension and the power steering systems are operational they will not activate. The vehicle would be drivable but only just (this would be true of lots of vehicles unfortunately). Due to our criminal/army friends visiting overnight it also be low on fuel, not that you need much for your current mission and a resourceful team should be able to find more. 

If you wanted to make use of the vehicle long term as a sort of base of operations your team should have the skills to fix it up and even upgrade it if they're willing to put in a little time. I would defo recommend upgrading it if that is the plan however as a bus isn't exactly low profile and those things are flimsy as hell, not to mention there'd be something of an excess of chairs...