The downside to individual servers, and micro-communities, is the cost and maintenance of lemmy instance. Its more scalable, reliable and cheaper to have a bunch of relatively low-churn communities exist on one bigger instance.
The upside is that the rust community gets to own its own data. If programming.dev decides to shut down tomorrow, and posts and comments made there are gone. Lemmy doesn't mirror or cache... all that data lives solely on the server ran by somebody.
I'd vote lemmyrs at least for now until a governance and stability model is figured out to ensure these conversations don't go into /dev/null like /r/rust (sort of) did.
If say the Linux Foundation or a similarly large open source foundation (Apache, FSF, OSI, etc) decided to host a larger "open source" server, I'd consider moving there to improve discoverability and lessen the burden on the rust community itself
I always recommend opensuse for ex-windows admins because it's stable, long term version (don't need to move to a rolling model that tends to confuse people), but most importantly YaST. It's a big ol do everything GUI for managing the system