OpenWRT does not use liblzma or systemd so i think that one is pretty safe. I would also be surprised if Android included OpenSSH server binaries in that way.

this is extra tricky because they did not specify the exact kernel. mainline could be any of the kernels tagged as stable that you can build from linus’ git tree. i know that in the past you could run a mainline linux on intel 368 chips but today you probably can not because official support was dropped a while ago.