Microblogging and/or long-form but clean sheet. Don't show any existing users. And no discovery. You can only build your network from people you proactively add.

Many people who give Nostr a go see the top trending posts are all Bitcoin laser-eyed cyborgs--and that's it, they're out, goodbye, never to return. For those people it would be better not to show anyone or at all, no activity at all. Have it all blank.

Market it as a start-from-scratch concept. Build the whole UI around a clean sheet of paper ethos. (If you think about it there are a lot of UI decisions that would be driven by that.) And emphasise self-ownership above all else. And interoperability to follow--but limit the interoperability to other clients that are also clean sheet, such as event booking for friends a person has already added, or some of the existing chat clients that by nature are clean sheet.