there is nothing wrong with it, most microwaves have that option and do not have to be vented out, even though as a contractor i prefer them to vent out. if the existing pipe already vents out, which it probably does if there is a pipe in the cabinet already. what you would have to do is unscrew the 2 or 3 screws in the top cabinet that screw down into the microwave ( if not there then there may be 2 bolts in the front of the unit behind the cover that have to be loosened) that will loosen the microwave, then its a matter of taking the screws out that hold the fan at the top back, pull the blower fan out and change the direction so that it faces up, screw the fan back to the unit and put the microwave back up and bolting it. check to make sure the fan connects to the duct work, if not, add a piece of sheet metal to connect and seal that joint. btw you may want to unplug the microwave before doing so, just for safety reasons.

The food here is incredible, and cheap.

The work they do goes beyond the aesthetic and includes health and safety as well.

Also, for tenant safety, does the basement have two entrances? 

Safety is number one.

You’ll need to sell some food, sandwiches, muffins, etc  too I would think....coolers, display cases/coolers, dishes, dishwashers, supplies, costs for labor, rent, utilities, insurance, licenses, permits, inspections, etc, etc.

That is going to be relevant to how in-demand your market is (which I have no insight on) but just food for thought before you panic too much. 

Industrial facilities are bound by more stringent building codes restrictions for fire safety.

It had food exploded all over the kitchen walls & ceilings as the owner would simply heat cans of food on the decrepit gas stove.

Maybe we can grab beer/food and talk REI.