#1 Is this bluetooth compatible, meaning i can connect to a BT-1 or BT-2 module?
Yes to the BT-2 module.
#2 Can this be mounted outside; can it get rained on?
TNT48185. We would not recommend the Renogy Elite 20 to be placed outside. As it is not rated to be water resistant or water proof.
#3 Can this controller be used with a automotive battery?
Yes. Standard automotive batteries are usually lead acid or AGM, so it should work just fine. Just changed charge controller settings to the correct battery type.
#4 How do you turn on the backlight on the 20amp? Manual says its backlit but it never comes on in any mode active use, scrolling, etc.