TPMS doesn't need to be unencrypted like that, although many car manufacturers do like to save a buck.
If you get a car old enough, you won't need to worry about TPMS (but that car will not have been tested against recent crash test scenarios).
Depends on the TPMS implementation to be honest. Most of the UHF ones are impossible to receive unless you're using some optimally placed/pretty powerful equipment. Even then, the protocol is entirely up to the vendor, as long as the system is reliable.
My car is old enough that it doesn't have TPMS sensors but I have looked into third party ones. It looks like there's all kinds of systems, from custom UHF to Bluetooth LE. No idea what your car uses.
TPMS is over the air, each sesnor has a 32 bit unique ID. you have 4 per car... its easy to identify