Any AR you bring up to Mass must be AWB compliant. No flash hider, fixed stock, no bayonet mount.
That is the case no matter what Maura says.
Do you have a Mass LTC? If not, you can't even carry any handguns you buy in Florida - once you bring them up here.
Where is your drivers license?
You can't have a drivers license in 2 states.
If you now have a Florida drivers license, you need to tell your Mass LTC issuer that you moved and your Mass LTC would become void - (not sure if you could still carry).
I think you Florida Non-Res CCW license will be good enough to buy a gun in Florida.
A Mass drivers license would not work.
If you buy an AR that was not in Mass on July 20th 2016, you will be in violation of Maura's AR ban. As of yet, however, nobody has been charged for such an offense. Could be costly if you become a test case.
If I were you, I'd keep the FL stuff in FL and the Mass stuff up here. Don't give up you Mass drivers license or else you wont be able to carry in Mass with your Mass LTC.
If anything I said is wrong, I expect a correction from @LenS who is an expert on this subject.