No real lessons learned. I like Go, and I like that it lets me do no-fuzz-straight-to-the-point development. The single Go binary and server is handling the traffic just fine, and the architecture is simple and easy to extend.

I am suffering a little right now while I try to add E2E encryption, because I structured the handlePublish logic awkwardly. But other than that there have been no surprises.

Sorry that's such a boring answer.