Building / CI / Nightly releases
Good news! The free GitHub tier is sufficient for both nightly builds and ISO creation, as well as CI builds. The CI builds run every time a pull requests is created. Both processes do a full build, and even boot the image to a QEMU virtual machine to ensure it doesn't hit KDL.
So at this point, we won't need any other build servers or paid products. Eventually, we may want to look at leaving GitHub or setting up more advanced build servers to do stress-testing of the builds, but it seems GitHub is sufficient to get started.
Unless there is any objection to this approach, I will update the documents accordingly.
Packaging
This one might be complicated. Most .hpkg files built by HaikuPorts declare a required haiku version. If RenkuOS doesn't provide a haiku version, the package solver can't resolve that, so pkgman and HaikuDepot both refuse to install it.
(Installing is the issue, not running. A self-contained app you copy across will still work, as clasqm pointed out in the original thread, at least until there is a ABI or dependency issue.)
We could provide both identities.
provides {
haiku = r1beta6_hrev60071_15 compat>=R1beta1
renku = 26.9
}

The haiku value would be our fork point. Their packages resolve against it; RenkuOS-specific apps would require renku instead, which also means they won't install on Haiku.
This preserves compatibility with packages built against our fork point or earlier, but it is not permanent. HaikuPorts rebuilds against newer nightlies, their base level may pass what we claim.
This gets us running now, but it doesn't remove the eventual need for our own repository.
Open to comments and feedback.