I did this with Ubuntu rather than Debian, but the debootstrap process is the same. You’ll want to follow the steps in https://wiki.debian.org/EmDebian/CrossDebootstrap, and then do the same post-configuration as is done in the wiki instructions for creating an Ubuntu root filesystem.
You will need to either use Globalscale’s kernel and modules (extractable from their Buildroot rootfs) or build your own kernel (following the instructions on the wiki). Note that doing the latter will mean you won’t have working wifi drivers, if you bought an Espressobin with the Marvell wifi card.
