If you’re willing to do the full VPS route like it seems, check out Hetzner. In my experience, it has higher resources at a lower cost than other providers like DO.

If something like multi-reddit comes about in Lemmy, I believe it could solve that issue. Just make a multi-reddit of what is the same community (roughly) over multiple servers. It won’t solve the problem of duplicate posts though. But Reddit had the same issue at times, where multiple subreddits for the same topic existed, although generally it merged down into a single subreddit that was actually useful.