My instance is close to two years old now, and on average has had about 2 MAU, with no (local) communities.

Currently we have about 700 active federated communities (that had any federated activity within last month), out of 900.[^1]

The on-disk size of both lemmy and pict-rs database[^2]

postgres@postgres:~$ pwd
/var/lib/postgresql
postgres@postgres:~$ du -sh data/
31G	data/

I use pict-rs with S3 provider and the bucket size is currently at 22.82 GB (this is probably mostly just thumbnails).

So in total there is almost 54GBs spent just for lemmy.

So assuming you have 100G remaining after system stuff and dedicate that box only to lemmy (and pict-rs media files) and use it mostly for yourself [^3], you should be alright for about 3-4 years (assuming that I am gaining about 27GBs total per year and that you will federate similar amount of similarly active communities).

[^1]: The rest is either dead (instance gone) or no one is subscribed to them anymore (as such my instance is not getting any new content from there: neither posts nor comments or votes)

[^2]: Postgres itself reports about 2G less, don’t really know why but I am guessing it has something to do with the filesystem being btrfs

[^3]: You should use Lemmy Subscriber Bot to automatically federate little bit of random communities so that public All feed is not exact copy (minus NSFW comms) to whatever you as the only user subscribe to.