I run a misskey server on a VM on hardware dedicated to
our stuff - we control the hypervisor on the boxes, we "own the IP space", manage backups, etc. Misskey is a federated activitypub instance; and in my opinion it is better than mastodon at being a "twitter replacement."
I checked the dashboard for my four user instance (myself and 3 others, total) and we're currently pub/sub to ~~5200~~ 5219 instances. I added a curated list of "journalists" across the federated activitypub realm, around 1300. So now i have basically the "news" part of twitter, 24/7, without all of the jokes, memes, and trash found on twitter. I also am on fosstodon, but I maintain that as a backup for another mastodon instance i have an account on, where both the maintainer and the public face of the instance have a "you get what you pay for" / "that's tough, suck it up" mentality toward maintenance and downtime (they're approaching less than 1 nine for the month of april). I am unsure of how many accounts fosstodon has, the local feed is pretty slow, so i'd guess between 1000-5000 users, the other mastodon instance is capped at 10,000 users, and a job removes everyone who has not logged in for a year, and signups are once a year (and maybe a thing of the past, to hear the "leader" talk).
I really like misskey. I'd probably like something else more, as i can't admin misskey competently - most of the online help, advanced documentation, etc is in Japanese.
For the record: currently 600GB attached; 130GB used, 24GB for / and 105GB for the misskey/files folder. It has 8GB of ram and 4 threads; it uses all 8 without OOM, and ~5% of the CPU. I don't really know the network throughput, but it's on par with a webforum with 3600 uniques per day. activitypub and the fediverse allows for more multimedia to be shared, faster and with less friction, so that explains some similarities and differences i see between these two decentralized services.