Using the DFU Target Library

We use a custom board implementation based on nrf52840 that makes use of a proprietary host transport protocol.

I am trying to implement  FOTA using our transport. We can successfully download the app_update.bin file that is created when using NCS to create the boot images.

I would like to confirm that by using the DFU Target Library I can update the image slot and reboot to the new image.

Is there anything special I need in order to do this?

Second question:

The app_update.bin image is downloaded to external flash. Could you possibly provide me with suggestions as to the external flash configuration should I wish to specify the secondary slot for DFU. We are using QSPI with an MX25R6435FM2IL0 flash chip. The image is downloaded to an offset of 0x300000.

Thank you