I have a server set up for a small Discord channel, and since we're all in different time zones, there's not many times when there's more than one person on. This server is set up on a Pi, it runs fairly smoothly, but I have no idea how many people it can support. Probably like ten-ish at a time, max, but this is kinda proof-of-concept.
If you wanna join, post in this thread and I'll PM you the address. Standard rules; no griefing, no being a dingus. We're running some anti-griefing bukkit plugins, and if there's issues, we can set up a backup script. Other than those plugins, it's pretty much just plain old vanilla.