The 100s are a good match sound-wise in either TV or music modes.

the 300’s Atmos really comes down to you and what you watch. I do almost none so for me it is a no, but others here do a lot and think it is worth the cost. Even the cost of getting the Arc for better front Atmos sound.

The One SL’s are also a great choice. I had the 300’s and returned them. Prefer the One SL ‘s. 

My personal choice would be to add the Era 300’s, but these things can depend on the listening environment and so without detail about that, I would choose them as they are the better sounding speakers in an ideal environment. Meanwhile you may find the following two things perhaps useful to help you to decide…

https://www.sonos.com/en-us/blog/the-ultimate-guide-to-a-sonos-home-theater