For transparency and in case it helps people considering whether to self-host a similar #Mastodon instance, the operating costs of #ResPublicae are currently a little less than 25 €/month (VAT included).
Without any performance optimisation whatsoever, the instance is currently quite overprovisioned and should have enough capacity to withstand over 1 year of growth.
Using a smaller instance would cut hosting costs by some 10 €/month, but reducing #MastoAdmin time costs is more important.
Update: the object storage grew to some 500 GB but the costs are still around 25 €/month. CPU and memory are still quite overprovisioned.