Speaking of traffic, if I were interested in running my own federate, what can I expect in terms of loading and where is the content actually stored, my single instance or distributed? I see the reqs. on RAM and CPU utilization but I'm actually more curious about usage data.
It depends on many parameters. Data from your users is stored locally. But then you have federation: every time one of your users subscribes to a community of another instance, your instance will cache it locally. You can manage how much cache it uses, but the cache is there of a reason.