I had a similar curiousity… Like if I make my own instance but it’s just myself, is that even a net positive to the network? Now there’s a new instance pulling everything I want to it, rather than another bigger instance that might have used that share subscriptions…

It’s probably optimum to have hundreds to low thousands of users per instance but it’s going to depend entirely on the level of overlap the users have in terms of external communities they access. If you have 1000 users each subscribed to a single different community with no overlap, then there’s no benefit at all.