Livechat or authenticated user chat?
The former is just a matter of enabling and configuring Livechat in Rocket.Chat, then including a javascript in the HEAD of the HTML. There's a plugin for it on WordPress.org but it uses deprecated URLs, and it's overkill for a simple JS addition anyway. Just add it with a function. Here's the docs:
https://rocket.chat/docs/administrator-guides/livechat/
The latter is a bit more involved, I found this page which covers some of the process but it's not WordPress-specific. Might get you started though:
https://mohammedlakkadshaw.com/blog/embedding-rocket-chat-using-iframe-auth.html/
> Running mongo local to a Pi is not recommended at this time.
Yes it will definitely install with some effort.
Mongo isn't known to be the most durable database, and keep in mind most SD cards aren't designed around that kind of usage.
You also need a 64 bit OS, so most Pi distros won't run it since they're 32 bit.
https://andyfelong.com/2019/01/mongodb-3-2-64-bit-running-on-raspberry-pi-3-with-caveats/
This tutorial notes that 2G of swap was required to avoid hangs and crashes.
Is it working for you? How many users? How big a DB? Just curious, really, because I used to run a 3 user server and I want to say it used a couple of GBs of RAM easily between Mongo and the Rocketchat server.
Yes, that's not a problem:
mongorestore