While we live in the area, our goal is to make these STRs as self-sufficient as possible so that 1) the cash flow they generate becomes increasingly passive, and 2) we feel confident investing in STRs out of state, which we’d like to do in the future.

Of course it's very difficult to find good deals these days, but if you find a deal that meets your buying criteria then there's likely not a good reason not to buy it, unless you don't have sufficient reserves to handle any surprises that come up shortly after purchasing.

@Marc S.Note investing is just another strategy in the vast realm of real estate investing.

Get another electrician. 100A is not sufficient for modern loads.

Do you think doing the following will be sufficient to convince the judge NOT to prosecute the landlord in the event of a gas explosion that cause injuries or even death to tenants?

As long as there is sufficient advance warning, that has proved to work best. 

Make it HURT for the tenant to remain.Be sure to do a substantial hold-back of funds at closing sufficient to cover the per diem and eviction costs and do a final walk through on your way to the closing to be sure that the tenant is gone.You can solve the "secret verbal lease" issue with an estoppel certificate. 

Contracting a property with no where to turn for money except a vast land of real estate forums is not a great sign. 6% is a terrible return, it's less than inflation.this is a tough one.

Is a certified and proof of receipt postage sufficient to meet the requirement to notify the tenant?

As long as the metal box is grounded and the ground is bonded, a pigtail or a grounding clip is sufficient.