Welcome! It sounds like you're in the right community :)
For the first challenge about power loggers, I recommend starting a thread on this topic in our Wildlife Tracking group - I'm pretty sure we have some members working on loggers that might fit the bill (and for that matter, members that are interested in a similar solution), so that would be the place to get in touch with them. In my experience, the more info you share about what you're looking for the better. If you go ahead and do progress on designing your own open source loggers, this thread would also serve as a nice place to share updates about the progress of the project (as Neil and Arik - part 1, part 2 - have done in their ongoing projects).
As for your interest in open source acoustic montioring - you're already involved in the Audiomoth group purchase thread, so great! The machine learning question is an interesting one, it might be worth starting a thread on this topic in the acoustic montoring or machine learning groups (either will work) - I know there are members working on this individually, but there isn't much discussion (yet) about it. Perhaps you might kick it off?