A:
Note you only need the connect amp if you are adding speakers that are not from Sonos, or that are not amplified speakers. you can connect any type of speakers you would like, as long as they are not amplified speakers.
No you do not need a volume control it is in the mobil app that you download.
you control your volume with your phone or computer or tablet or whatever you want to use.
if you add a stereo make sure you use Sonos Connect, not Sonos connect Amp.
To control your volume you just set your volume control on the stereo were you would like it, and then you can still go up or down with your app.