CRS312-4C+8XG management port

Trying to understand the default port settings/assignments.

The CRS312-4C+8XG has a extra MGMT port which i understand is the out-of-band interface to manage the device.

The MGMT port is on the hardware switch2 and with switch1 in the default bridge group - why?
When bridging together with all other interfaces i do no longer have an out-of-band interface anymore.

The default ip of the device is set on the ether1 interface - why not on the bridge?
And why not on the MGMT interface where it would make the most sense?

In the interface list the MGMT port is assigned to WAN, does that mean someone would connect that interface to the internet for management?

Thanks