So to buy out an $84 annual lease created in 1900 you would divide the rent by 0.06 = $1400.

This was very informative as I own 14 acres and was thinking of dividing them and putting 2 bedroom apartments on it.

Off the Net Operating Income, divide that number by 12, for monthly income.  

TurboTax Premier and higher versions will handle the situation you describe.When you rent out part of your property, you divide certain expenses between the part of the property used for rental and the part of the property allocated to your personal use, as though you actually had two separate pieces of property.  

The way I came up with the numbers was using a conventional amortization schedule and summing up the total amount of interest over the term of the loan (360 months), then dividing that amount over 360 to come up with a fixed monthly interest and hence a fixed capital amortization.

Everybody has their own strategy - here's what I do:Property Tax Reserve - this is simple...take your estimated property tax and divide it by 12. 

Hence take your budget and divide it up over that length of time.

Then you can divide that number by your floor area and see if your way out of line vs nearby comps.

The trick is, I too am busy with running jobs that has in-house crews, so I'll simply act as your typical GC or commercial GC / paperwork contractor on this to divide my time, I could fill out the gaps but I couldn't use majority of my workforce because i have deadlines also, i could fill in a tradesman or two when there's a hiccup, say when a plumber or electrician doesn't show or keeps pushing the schedule out, but that's about it.

That cost can be added in as a separate charge on each lease, divided among tenants according to the size of the unit they lease; but that charge needs to be referenced in the lease agreement.