Looked over your other post,
Your instance A replicates or really caches the content from C@B indefinitely, if you are subscribed to it (or if anyone on your instance is subscribed). When you make a post on C@B your instance transmits that post data to B. Other instances subscribed to C@B will get your post when they receive cache updates. As long as the instances aren't overloaded it is a pretty snappy process in my experience.
Pictures are not replicated but hosted on the instance of the user posting them. Post/Comment data is cached. Your instance will store a cache of all the subscribed communities. Even with a large number of subscriptions all that data is just text and gets filed into the database without consuming much space at all.
Edit: just some things I've read while setting up my instance. Pretty sure that's accurate.
Chicago95, awesome! I love the retro style. I've never checked out DWM but I used to use i3wm. Loved the power. However, I always keep going back to xfce. It's just the most comfortable for me.