Lots of experience with it, long time engineer, I have in the past made my own drawings/permits and gotten them approved by reading through city regs/docs.

I'd specifically explain that the HVAC is the only allowed heat source, no other appliances are permitted,  and if it's not powerful enough, suggest you guys part ways.     

Use extra screws to secure the cabinet to the wall even better.

It has little extra land for storage units or pumpkin patch to bump revenue a bit. 

Are you saying that for example if I just threw that $115 extra toward the principle every month it would benefit me more?

For your situation I’d have him pay an extra month, keep the deposit and let him leave.

The land is free and clear so no extra cost. 

Pay it off as scheduled and then leave it and collect the extra cash

https://www.irs.gov/businesses/small-businesses-self-employed/tangible-property-final-regulations#SafeHarborElectionforSmallTaxpayersSafe Harbor Election for Small TaxpayersYou are not required to capitalize as an improvement, and therefore may be permitted to deduct, the costs of work performed on owned or leased buildings, e.g., repairs, maintenance, improvements or similar costs, that fall into the safe harbor election for small taxpayers.

However; what you can do is look up the number of permits that are pulled from the building department, most cities have that online now.