If, on the other hand, this makes use of some Nylas-hosted server, I'm a bit bummed out, since this would mean all my data is transferred through Nylas servers.
Which is it? Or should I just bite the bullet and read the source?
We're working on putting together a better doc that outlines how to set up the entire stack locally. Ideally this could even be a Docker container.
And you should always read the source! ;)