Little summary from our instance in numbers (20221107):
🔘 Mastodon version 3.5.3
🔘 Active users: 35
🔘 Interactions: near 1k
🔘 Disk: 26Gb (90% are media_attachments)
🔘 DB: pg_dump recently baked is about 200Mb (50Mb gzipped)
My guess is that no big investment is needed - server - for a tiny number of users, but to be honest dunno what happens if it grows as it is doing in some instances that have experienced problems lately.