@eller82 DB size doesn't count towards the disk space limit.
The main usage of space for small instances is remote cache, that is cleared every week. See: https://github.com/tootsuite/mastodon/blob/master/lib/tasks/mastodon.rake#L47
But it really depends on the community, if it uploads a lot of gifs and images, it can go fast. If it uses mostly text, then it can last a long time.
Still, adding extra space is cheap.