Honestly, I'm interested in knowing some of this too.
https://join-lemmy.org/docs/en/administration/administration.html says about 150GB RAM and negligible CPU usage.
I assume an instance with users subscribed to active communities requires meaningful storage, but I'm not clear the sizes we're talking about (what's data growth per/day been like for some of the larger communities).
EDIT: Likewise, I'd love to know if that 150GB RAM is fixed or whether that number grows with use.
I had a candidate actually do that for a similar problem.
They were like 15 classes in to generate fibonacci numbers, it was wild.