Three notes from #new folks here.
For iOS: Use the iOS web app. The iOS mastodon app does not make use of many of the new features in v4. The iOS app will get better soon and we'll announce that.
Remote follows: Try withdrawing a pending request and then follow again. Sometimes a remote instance isn't able to send us back a confirmation acknowledgement.
DM: Direct Messages are created by starting a post with @. In the web interface these show up by tapping on the @ sign on the right.