I am imagining a worst case scenario where we come to the closing table ready to purchase the property and the investor has cold feet and withdraws the money from escrow and we are stuck losing our deposit.4. 

Why would you WANT to put a higher deposit down than necessary?

In some of our areas the water is "hard" and creates problems with mineral deposits within the appliances.

If your bank has a lot of local branches, you can also ask your tenant to direct deposit their rent at the bank in your account.

Are utilities included, pet deposit?

You will lose your deposit if you can't make the payment.

If you do, just make sure you have all paperwork for current leases, sec deposits, from tenants for past 2 years. more than likely you won't have the verification from tenant that says they agree to what's been paid, a Estopple but honestly come hell or high water if you want that building your going to take the opportunity now that gets you the property and deal with any tenant changes that may come up if they remain.

I am imagining a worst case scenario where we come to the closing table ready to purchase the property and the investor has cold feet and withdraws the money from escrow and we are stuck losing our deposit.4.

The deposit should account for the eviction and lost rent unless that was less and if they took 1 month rent it probably wont.  

I wonder if they charged her a second security deposit?