If they are not friends and all on separate leases then yes I would change locks if I don't get key back in a few days.If other tenant is going to clean room for free because she wants that room then I would not charge the one that left a cleaning fee.

Your cash flow is basically rent minus mortgage P&I, property taxes, insurance, income taxes, local fees, utilities (if you pay any), repairs, management, vacancy, evictions and capex items.

If you assign a contract and earn an assignment fee, you should have already made more offers.

The asking price for the home is 132k.OPTION 1 – Cash After Repair Value = $132,000 (estimate)Discount 80% of ARV = $ -26,400Repairs (Price per square foot) 1,190 x $5 = $ - 5,950Cash Price (seller pays closing cost) = $99,650OPTION 2 – Sandwich Lease Option – “Perfect Tenant Program” Term: Minimum 5 yearsOption Price (buyer pays closing cost): 125,500Option Consideration (non-refundable fee we pay you): + $500Monthly Rent: $950 (profit + $100 cash flow per month)Total profit (If completed full term): $132,000Note: We are the tenant-buyer, but we will sub-lease the house to another tenant-buyer.

Please look over the terms of the loan or balloon payments or other fees.  

What can they give me in terms of data--rent history, leases, repair history, their fee on the property, historical turn and fill rate, avg length of tenant--all that kind of stuff.

What fees are associated with assuming a commercial mortgage and how long does the process typically take?

That solves the variable interest rate problem and allows you to pay off the HELOC and use it for the next one.In addition, most HELOCs have very low fees.

Charge them a fee for using water or electricity IF you pay for either. 

If it is to help you fund a deal, that can be a very risky strategy.If it is to make it easier to track your expenses, almost any credit card would work but I would recommend one that doesn't charge annual fees.