It allows us to pocket a pile of tax free cash from the sale of our primary.

You can use 1 EIN for both since you are DBA under holding co LLC or if he believe you should get a second LLC EIN number for tax purpose. 

Keep using your 2/5 primary no tax up to $250,000 and your basic rent offset cost for the investment.2.  

You can go in and offer the county practically nothing for it, but it means more tax revenue for them, and no one would ever build a house or outlet store there.

After expenses and mortgage, I end up with a net cash flow of anywhere b/w $150-$250 which I find rather small, and I wonder if this could even get eaten up by tax filing time.

A lot of areas are cracking down on STR and/or charging fees (taxes) to run one.

I have investments in Loudoun and one in Clarke County doing extremely well but bought everything in 2008-2013 and have been hibernating since..looking further out in Charles Town WV specifically because of location closer to Northern VA also the taxes are cheaper.  

Verify if there are any outstanding violations or issues that need to be addressed.Financial Analysis: Review the property's financial records, including income statements, expense reports, tax assessments, and utility bills.

I think some markets, mainly the STR runners, have another 10-15% to go then the markets hit by HOA/HOI/Taxes still have a bit more correction to go for. 

I'm not ruling out Florida, but it isn't my focus because of taxes and insurance costs.