Upgrading Playbar Setup to Beam Setup

First Things First….😊

1. Do not factory reset any Sonos speakers
2. Unpair the Ones’ and Sub 3 from the Playbar before disconnecting it
3. The One’s should revert back to individual rooms and not a stereo pair. If the latter occurs (although it should not) remove them as a stereo pair.
4. The Sub 3 after removal should appear as “Unassigned”
5. Now remove the Playbar and set it aside
6. Reboot your router and let it come back
7. Power Cycle your device
8. Using the App Install the Beam 2 using the supplied HDMI cable using the HDMI eArc port if available. If not connect the Beam 2 to an HDMI Arc port. Test the Beam 2 for audio.
9. In the room with the Beam 2 select add surrounds
10. In the room with the Beam 2 Select add a Sub (you should see your sub as Unassigned)
11. In the App set your surrounds to Full Stereo for music if you desire. They will auto switch back to surround mode after the music has stopped.
12. Test your Sonos

To your second question….

IMO, The Era 100’s are a better speaker than the One’s. However, only you can decide if they sound better than your One’s. Personally, I don’t think Sonos would have designed them to replace the One’s if there were no noticeable difference/improvement in sound.

I have a Beam 2, with Era 100’s and Sub Mini setup in a guest bedroom. To my ear the sound is better as surrounds for movies and music. I also have Era 100’s as a stereo pair with Sub Mini in my garage,

Note: As with your Ones’ the Era 100’s cannot be used independent of a soundbar when used as surrounds.