PM Self-Serve account and PM Community account are separate things.
They can have different email addresses if you like. But they need same email address to link Self-Serve billing and Community Rewards.
Community username must be public. Community email is not public (unless user changes setting). Self-Serve user information is not public. The PM Moderators (employees) do of course have access to all private user information.
You don't have any ability to change Community username - unless you can get the Mods to do it for you - although you can always create new Community accounts with different email addresses. And you can already use the same login for both portals - Community username can be your email address for both - it would then be visible to the public and if you don't want that then you'll have to change something anyhow, end result is different logins at different portals no matter how you do things.
There isn't any real advantage to keeping them different, only you (and the PM Mods) could see the difference anyhow. If you're concerned about security, privacy, or anonymity then forget it anyways - smartphone, SIM, account, and service are already linked and logged and tracked when active, the best a tinfoil hat can do is use an anonymous email address, not volunteer any personal info, and pay offline with cash only (at random stores with phone turned off, haha) wherever possible.
