1 - yes, it basically consist of a box with a keyboard on it. Not sure how long the link stays alive but this is the one I got:
You need the keyboard to teach the device which fobs it should use. I’ve received 10 fobs and I had to set them all up so they’d work with the system. It is a simple key press procedure.
You could potentially just hide the actual unit behind a piece of plastic somewhere so the keyboard is hidden after that. As long as the RF goes through whatever it is hidden behind (like plastic), it should work fine.
2 - the distance is about an inch. It uses RFID tags – similar to the swipe keys you use to pay at certain gas stations.
3 - Shouldn’t be a problem. You can probably put the disabling relay in line with the thin wire going to the starter or the +12V of the coil. It would have the same effect.
It will require a bit of McGuyvering to get it to work but mine works like a charm with my house alarm system.