Access - I have been advised that the staircase and railing leading to the attic will have to meet code and be sturdy enough to support the tenants4.

Usually rentbacks call for higher rents than market, not lower. of course, those situations I've seen have always been short term. you make it sound like this can be several months. in that situation, I would tell them they have to pay market rent, and provide security deposit.

No access to base, but live just outside the main gate.  

I purchased a duplex and want to submit my appraisal to the county in order to hopefully lower my taxes.

I like LoopNet and 100% agree on the establishing the relationships to gain credibility and access.

Plus we're likely talking gmail or similar free service would they even allow (not that it would be cost effective) IT forensics  the access needed to show?

I can give you very high level calculation to understand both scenario...Lets say you buy 100K house with 1000 rent... lets compare all cash against leverage...All cash InvestmentYearly return = 12000 (Rent) + 2000 (Appreciation) - 3000 (Tax + Insurance + Capex) = 11000 = 11%LeverageYearly Return = 1000 (Rent Cash flow) + 2000 (Appreciation) + 3000 (Amortization) = 6000 = 6%Now when you leverage investment at 20%, you can buy 5 house from 100KYearly Return of 5 Houses = 6000 X 5 = 30000 = 30%There are more tax benefit in this deal also as your positive cashflow is lower...If you are planning to buy multiple houses, Leverage is always better...

Today I went back to the apartment to check up on things and I noticed that the pay or quit notice that I put on a door had been removed so I know someone has been there inside but I do not know if it was him or maybe a friend of his that has access to the apartment.

I believe both have to be accessed through an Agent but I could be wrong.

Modern, direct vented, natural gas and propane furnaces are typically in the range of 92 - 95% efficient.Your decision on whether to replace the furnace will depend on the efficiency of the current unit and whether it make more business sense to replace the furnace or to add a heat-pump with an exchanger insert to the existing system ... and, it is (or should be) primarily a mathematical decision yielding which ever approach is going to offer the shorter payback and lower operating costs.The math aside, there will be other non-math factors.