Your surround setup proposal is not possible. Separate LF and RF are not supported. ARC is L-C-R. The surrounds could be a pair of SONOS powered speakers or an AMP driving two rear passive speakers. One or two SUB’s could be incorporated. Additional surround speakers are not supported.

ARC and ERA-300 provide height channels.

I’m not sure what you are expecting with “ambient sound” in other areas.

In the SONOS parlance a “Room” can be a single speaker, a “Bonded” stereo pair of identical speakers, an Amp, or a Bonded collection functioning as a surround Room. You could certainly place additional speakers in a physical room, but they will not be part of the surround audio processing. In a SONOS controller they will be separate Rooms. Rooms can be “Grouped” to play the same music and will be time aligned with each other. When the surround Room is playing TV audio there will be a slight time offset for other members if you Group TV audio. This time offset will fluster your ambience scheme if it is intended to be used along with TV audio.

@buzz I have an open floor plan where the family, dinner room, and kitchen are on the same area.

I would have three zones, 

Zone 1 - Family - Arc, In ceiling, In wall

Zone 2 - Dinner - One pair of in ceiling

Zone 3 - Kitchen - One pair of in ceiling

“Zone” in your parlance becomes Room in SONOS parlance,

Your concept of using both wall and ceiling speakers, connected to the same AMP, is not a great idea in my opinion. The surround will be diffuse.

Therefore I don’t approve your Zone 1 configuration.

The Kitchen and Dining rooms are fine. Be aware that you will bump into the time offset issue if you attempt to Group Kitchen, Dining, and Family while playing TV audio.