Anyone have a good workflow worked out for building a Meltano image via Github Actions where some taps/targets are pip installs from private repositories ?

Yeah, we put our custom taps / targets are in the meltano project and pip installed locally. Works on gitlab CI, should work on GitHub as well

Yeah that probably makes the most sense. I've got a couple separate meltano project repos I'd want to use the same custom taps in, but I suppose submodules or something like that could work.