Many states land records are on line.

I have tried cold calling and researching online, but I have been shooting in the dark and all the responses have been that they are not experienced with it.

Moving to Quickbooks Online and producing a balance sheet and P&L helped a lot, it then looks like any other business.My new guy looked at the cash flow as not contributing to retirement income until the mortgages are paid off (my net with mortgages is trivial).

Go online and verify the bills.

The retailers that sell mostly to homeowners and thhe big box stores usually carry the value prices options but not always the best long term values. 

From what you describe, assuming that existing rental income is honestly reported on your tax returns, you should be able to count both rental income from the existing property, and projected rental income from the other units in what you are buying, assuming a local REI-friendly lender with minimal/no overlays (those are the reason why you see conflicting stuff online). 

Can the store lose it grandfather rights?

You can also check their reviews online at Google, Facebook, or Yelp.

These days, you can check Zillow and find out how long it's been on the market, so if it's on the market for over 90 days, they're asking too much.As to real estate taxes, figures are available on online, and can go up on changeover of ownership.

@Kelvin Tian here is a calculator that has an amortization schedule and what happens when extra payment goes to principle. www.free-online-calculator-use.com/extra-payment-mortgage-calculator.html