Lots of unknowns right now. The best might be to look for a VPS provider that allows scaling up relatively easily.

Besides some low hanging fruits that are being worked on right now, it is simply unknown as no Lemmy instance has so far operated at this scale. The techstack (rust and postgres) is relatively performant though. Main bottleneck is likely going to be the database for now.

It sounds like Lemmy may have difficulty being scaled that hard, that quick. There are some database-side performance bottlenecks (that are being worked on actively) that block high concurrency and activity, as well as limitations in how websockets are being used in the current version that can cause dropouts on very active instances.

Both of those issues are being worked on, and it sounds like the websocket issue is particularly close to being ready for release-candidate. It really sounds like the focus on the dev's side is to prep for a possible reddit exodus before the blackout that many subs there are doing- meaning, get the software running reliably and performantly, knock out any low-hanging fruit, etc.

I'd also love to hear admin experiences about bottlenecks and scaling limits they see on their instances and ways they've found to address them (besides throwing more hardware at it)