Laws vary by state. Here in ATL, the legal darkness depends on which window it is... front, back, rear, size of vehicles. I saw a cargo van with Florida plates that had the entire windshield tinted... not very dark, but it was tinted. I thought that was awesome. Not sure if it is legal, but maybe so in Florida.
Anyway, when I get my replica, I'm planning to tint the windows. I don't want people to see who is driving. I want privacy and a cooler interior.
I have always tinted my own windows, but I will probably pay a professional to do my replica.
I've never tried tinting plexiglass.