It depends on different factors like where the main listening locations are and how tall your ceiling is.

Perhaps this guide will help. It is from the manual for the Sonos Architectural in-ceiling speakers:

You also have the option of mono mode, where the spacing doesn’t matter except from a volume standpoint. You might try that if you aren’t going to be standing/sitting in the Stereo sweet spot.

Thanks for the help. It sounds like spacing is fine at 6 feet then. We’ll be standing in the kitchen and the different modes will help. 

It will be convenient to have the ability to adjust the Volume of each pair in order to overcome local noise sources.

I know of a kitchen that has closely spaced speakers. When you first walk in and look up it seems like there are too many speakers, but when the music is playing, the sound is great everywhere. You must walk around a bit and marvel at the evenness. If a pair was removed, the coverage would become “lumpy”.

So to be clear with three pairs and one amp I still can adjust volume control for each pair on the app? 

No, individual Volumes cannot be adjusted through the controller when all speakers are connected to a single AMP. You should install an “impedance matching Volume control” for each pair. This will allow adjustment for each pair and present an acceptable load to the amplifier.

Thanks! Could I use just one matching volume control and let the other pairs just be based on the volume set on the app? I just want one room to have the ability to be quieter than the rest.

Yes, you can make one room quieter that way.

You do need to place the control between the main speaker wires and the wires going to the speaker you want quieter.