Yes
Not a factory installed item, but you will find them in most as an add on. They were non retractable, basically just a strap bolted to the floor, see the related link for a place to get some.
5 seat belts 2 front 3 rear
no
1966
Yes
No, the 1957 Chevy didn't come with seat belts.
Not if they did not come from the factory with seat belts. If they came form the factory with seat belts you are required to wear them.
Whatever the vehicle came with when it left the factory is what is required.
Yes, they should be the same
yes they did, they had just a lap belt.
Seat belts, yes.