You might qualify for a partial 121 exemption (still avoid 100% of taxes) if you are selling because of health, work, unforeseen circumstances, and such. 

However, if you're the self-managing owner and landlord of a property, you control if any part of the water supply piping is changed, and you can periodically test your outlets when you change your batteries in the smoke/CO detectors every year.

@Brandon Turner, that's one heck of a battery life ;) I called the electric company.

A source of heat adequate for healthful living conditions.

Even the very poorest in America have access to food and shelter and free emergency health care.

Market agnostic of public health concerns, I’m wondering what my leverage situation would be; should I allow first property to yield a few years of cash flows before putting all of that into another mortgage or save first few years as reserves.

Mother in law has recently been having some health issues and we don't see her lasting much longer in the home.

Change the batteries once a year so far.

I don’t provide services, but the tenant WILL provide me  drug tests on request, their health history, emergency contacts, agreement to work a program, etc.And that’s (one of the few) reasons why I think my CPA is incorrect.

But generally, I would consider the health and diversity of the local and regional economy as a greater factor in investing than the size of the market.