FHA is pretty good about keeping their loan limitations in line with local market realities, with $774,050 being the current FHA loan limit on a 4-plex (see below, chart straight from HUD).

I would say build a chart of the time value of the money.

These are all questions whose answers will help you chart the way forward ... there is no one size fits all answer.From an operational perspective it is always pleasant to know that your building envelope is relatively efficient (insulated and air sealed); that building systems (electrical, plumbing, HVAC and communications are up-to-date and dependable) and that you have the ability to put accountability for resource consumption in the hands of the tenants.  

I think its wholly dependent upon precisely where you live and updated for property unique conditions.

My point - appraisers are nothing more than gut check on value and NOT a precise science, therefore if there are multiple offers within a short time of listing then the appraiser should agree with the market. 

It is very important that you find out precisely what this covers.

Either or both could be forced to stop working at any point in time.Risk level on this couple is off the chart.

I'd need to know more about how old the building is, what neighborhood it's in, etc, to give you a precise picture, but here are some issues.1) You don't include any cost for utilities.

Once you know where you are going you can chart a course.

The Case Shiller is an actual chart based on current historical numbers (chart #2, based 10 years).Even more striking is Case Shiller 30 year, (chart #3).