No, you don’t need a secondary USB Flash drive plugged in the BBBw.
The “node-beagle-boot” project, boot’s up a “blank” BBBw eMMC, into a “USB Flash Drive”… That “drive” window that popped up in Ubuntu is the eMMC on the BBBw. So use “Balena Etcher” to write you custom RootFs to the eMMC.
Remember you have a custom OSD335x board with a blank i2c eeprom, so none of my “Factory” images will work for you. You can try:
But I don’t think it’ll work, so it’s going to be up to you to program your custom version of u-boot.
In that case, these same rules will apply to your “u-boot, usb mounted” eMMC: https://www.digikey.com/eewiki/display/linuxonarm/BeagleBone+Black#BeagleBoneBlack-SetupmicroSDcard
Regards,