I've had mine up since 6/15 and in total between attachments, DB, and misc other stuff it uses just under 30 GB of space. I've also ran one of the subscriber bots for a couple days so there's who knows how many communities subscribed in total at this point.

Between the major parts, the DB is about 6GB the rest is attachments and such that could be wiped without any real harm. I'm hoping to see a 'purge data after X days' function at some point, or even better a 'after last interaction' so active posts don't get purged. No use keeping the data from some some simple meme that had 2 comments forever though.