Manage your property effectively, be especially careful in the area of safety, use common sense, and have a lot of liability insurance.

By disclosed, I mean have her sign something to the effect.  

If children are present, are the children well behaved or wild?

The following was found in a google search:When septic systems are properly designed, constructed, and maintained, they effectively reduce or eliminate most human health or environmental threats posed by pollutants in household wastewater.

She has a good job and shared custody of her two children, both of whom are well behaved.

I'm struggling in finding resources on how to effectively and accurately calculate the value of property as well as AVR.

The latter option would save you the out of pocket expense while effectively financing the cost over the period of the loan.  

If the borrower is well behaved, I'll board loan with FCI or another 3rd party servicer using the ABS platform with online and ACH capability.

IMO, it takes a certain personality type to be effective as a property manager on a larger scale.

If you lack knowledge of how your actions effect others you may never see the unintended hardships caused by what you do.