How do I put the included Bluetooth keyboard and mouse into discovery mode?

It's not a Bluetooth keyboard. But you will find a 2.4G wireless transmitter in the mouse and can plug it into the USB port.

If I have a Raspberry Pi 4b with 4 GB of ram, can I swap it out with the Raspberry Pi that comes with the crowpi?

Sure.

I would like to add a ups and power bank to the case. Could you tell me what would the total power consumption of the pi 4 and display would be?

12W. There will be a lightning signal on the display when it's running out of power.