I 'git clone’d the OpenWRT source from github and built it using ‘make menuconfig; make clean; make -j 12’ on my laptop which is running Debian. I’m happy to share the ‘.config’ file I am currently using which builds an ext4 sysupgrade image of around 312M compressed (it uses a 2TB partition).
I actually configured docker to be in /docker rather than /opt/docker and I have that mounted to an 80G partition on a 256G NVMe SSD.