Also seems like they like to stick on wealth taxes for rich greedy landlords and investors.

You can also explore Salem or bordering areas such as Derry or hereabout but they tend to be very high tax areas so that eats away quite a bit of returns and would not appreciate as well as more Boston central locations.

After that they would own a passive 40% of a rental that would pay them a tax free gain every few years.  

WC is great - great schools, lower taxes.  

The third building is on its own piece of land with a separate tax ID.

Since FL doesn't have an income tax, go with a MA accountant. 

Before going into this, though I would be very conservative in your analysis of cost to renovate and what you think market rent (along with increases in taxes and insurance) would be so that once you are ready to refi into a longer term loan, your DSCR is rock solid and so is your cash. 

Look not only what it would rent for, but focus on what the net income is after mortgage, property, taxes, insurance, etc.

Tax.  

Any other surprises such as higher tax rates, preservation requirements, flood insurance, etc?