Maryland’s DLLR site you mentioned is definitely a step in the right direction.

When you mentioned you did your homework on the turnkey property, if that were the case you would have had a really good idea what the property was worth before you offered on it (of course sparing the occasional rogue appraiser, which may be what happened to you... idk) and certainly before the appraisal.

As mentioned above do not focus on this number, at all. 

It likely means you have that amount of coverage when caused by another peril and as mentioned it's typically a significantly lower limit than other coverage amounts.If a pipe bursts, it will likely be covered. 

Like Thomas mentioned, leveraging your personal residence carries higher risk.

Having said that, rents go up over time and as you mentioned tenants are paying down the mortgage (with more going to principal over time). 

You mentioned about the difference between the purchase interest rate and the refinance rate.

WE dont pay a fee for the credit line as I mentioned just 1/2 point for each new loan..

One option I haven't noticed being mentioned is to auction it.

The things you have mentioned are simple, high level thoughts based on assumptions.