@Dwight Cook  first don't forget to have a estoppel before closing specifying what is rent/security deposit etc. for each unit.  

The seller is friends with the tenants, so no background check was done and no security deposit was collected.

Its ironic you dont want Section 8 when that's the type of secure tenant you would want in that neighborhood who would secure rents monthly.

During the process of securing the loan for our new home the bank asked me if I was going to keep my original home in Broken Arrow or sell it. 

Then I would try to negotiate the date by reminding her she agreed at first and incentivizing going on the 30th by security check in hand on move out day or something similar.

Pretty easy to nullify (or secure) an agreement with this kind of language.

You may need a separate bank account to hold the security deposit, for example of the latter. 

By having positive cash flowing investments you can begin to replace your active income, as well as take advantage of appreciation over time to leverage that equity to acquire more properties - and you can take advantage of all of this while using the bank's money to secure assets! 

But what if I were renting a single-family home on three acres with no neighbors in site and this guy offered to pay me a year in advance and a $20,000 security deposit?

I carried over there lease and security deposit with the purchase.