Putting FreeBSD's simplicity and minimalism in practice. Well done!
I have 3 comments if that's okay with you.
The generic kernel will be extracted somewhere like
/mnt/install/boot/GENERIC/ (IIRC) so you have to
# mv /mnt/install/boot/GENERIC/* /mnt/install/boot/kernel/
and remove the
GENERIC directory.
Creating a valid
/etc/fstab file or copying one from a similar setup may avoid an unpleasant system startup.
Optional:
/cdrom...
/cdromN directories are created by
sysinstall(8) and should therefore be created manually if needed.