new owner ... stock sound & bluetooth questions

[BMAN_128]

Hi all ... I'm a new 1 series owner and want to make some updates to the stock sound.

When I removed the battery cover in the trunk I found the Combox (see attached image). My car has the USB connection plug + AUX input but no Bluetooth capabilities. I'm assuming that this is the module to enable BT in my car (calls + streaming) but something is missing because my radio doesn't have any of the BT configuration menus. Am I still missing any hardware or is it just a case of coding?

I also have these general question about the stock radio setup in the car.

1. If I removed the stock head unit will I need a radio code to get it working again?

2. Can I add RCA capabilities to the stock radio unit (via some aux cable/harness that plugs straight into the back of the unit)?

3. How do I get a +ve signal from the stock radio to trigger the bass tube to switch on when the radio is switched on? Is there a +ve wire that feeds the Combox that I could use to do this?

4. If I disconnect the battery do I need to recode anything?

One last thing, what the big red thing onto of the battery (orange circle in the picture)?

Thanks in advance for your help.
Bob