Well these days cosmocc -mtiny is more like 120kb, now that our binaries support ARM platforms too (like Android!) and all the code I've needed to add to make sure Cosmo works reliably for a longer tail of edge cases. But that's saying a lot, since unlike these APKs cosmo binaries don't need a gigabyte JDK to run.
I don't think so. OpenBSD 7.3 works great. Their latest release broke APE in two ways: https://github.com/jart/cosmopolitan/issues/1263 I'm not sure if something like this is an accident. We might need to shift our support to something like DragonflyBSD, Haiku, or SerenityOS if OpenBSD doesn't want us there.