If you can't for whatever reason, you risk foreclosure or paying more fees to extend if your lender offers it.

Kind of disjoint issues;  Corporate housing vs AirBnb.Corporate housing is typically about a year's duration for an employee/family relocated for a temporary assignment. 

A little work netted her 30K in cash and 22K in available credit on her cards, most of which was interest free for an extended period of time.

SEC 8 tenants want to live in the neighborhood where their extended family lives, which generally trumps it being in a bad neighborhood if they don't have their own transportation.  

So at this point I have been inside and looked around.Rents in the area range from $750-$800 per month, and the financing I am working on is at 4% annually (still negotiating duration, which could be a deal breaker) with a private lender who would pay the entire cost (purchase price+renovations).

You would want a lawyer to review title to make sure there are no issues there, you would want a good inspector to make sure there are no structural or mechanical/electrical issues, the typical stuff for a residential purchase, but maybe go the extra mile since you are unfamiliar with the area and not there for an extended period of time to keep an eye on it yourself.

My issue has been mainly turnover, extended vacancy, missed payments, evictions, and tons of maintenance. 

Tonight I received a call from the husband, as I had been communicating mostly wife during the duration of the lease term.  

If you want to do that, sign an amendment to the contract to extend the closing date.

What ratio / threshold do investors use to ensure that hey are not over-extended?