I hesitate to be too critical without more information, but my initial response would be this is not what you should expect from a fully, proper turnkey investment property. 

What's the "critical mass" of tenants to make it worthwhile?

Know how to take constructive criticism.

If you're a single mom with student loans, a car payment, and living paycheck-to-paycheck, then $20,000 would be devastating and a reserve is critical.

To Avoid Criticism: Say Nothing, Do Nothing, Be Nothing + You miss 100% of the shots you never take.

This may seem obvious but it is absolutely critical.

Books On the Importance of Cash Flows – Critical to real estate investing.

As I'm trying to come up with estimated closing costs to run the numbers on potential deals, I'm trying to turn a more critical eye to the closing costs from buying my personal home last year. 

This will be a remote investment, so yes, a good PM will be critical.  

Not only should you not have to worry about tenant placement and rent collection - but maintaining and improving your asset is critical to protect cash flow.