For large instances pictures is probably the bigger consumer of space, but for small instances the database size is the bigger issue because of federation. Also, mass storage for media is cheap, fast storage for databases is not. With my host I can get 1TB of object storage for $5 a month. Attached NVMe storage is $1 per month per 10 GB.

For my small instance the database is almost 4x as large as pictrs, and growing fast.

If you have open registration you should reduce the account creation rate.

It runs /e/OS, which is very much a privacy focussed OS.

https://e.foundation/e-os/

The cheapest CyberPower/APC that is pure sine wave should be just fine.