You really need a soundbar for the tv sound. Arc will best fill large rooms with sound. 
For music, a pair of Fives are Sonos’ recommendation. 

You’ve not said what your budget is, but a Sub will add to the sound of both Arc and paired Fives, but a single Sub can only be bonded to one or the other. Buy one and see how much it improves the sound. Get a second if your ears can justify it; I’d probably just leave it connected to the Fives. 

Thanks Nik!

That’s the thing, I need to choose which 1 setup will satisfy the 2 use cases I described, and in the best way (or the least worst) .

A soundbar minimises lip sync issues. But, the way Sonos achieves synchronised multi-room audio is to create a buffer at the start of streaming an input. Bluetooth or line-in to the Era will have a 75msec delay. Some find that ok; others say the lip-sync is too far off. 
 

When will tv manufacturers introduce video delay options…

15x20 room, a Beam, Sub mini and a pair of 100s should fill that well.

For music consider setting the surround mode to Full for more sound.

Thanks Stanley. If I’m not interested in separate surround speakers, will a an Arc and Sub mini do the trick while also be decent solution for music listening? 

Like all soundbars I’ve experienced, the stereo separation/soundstage isn’t very wide, but the Arc is pretty good for music. 

Arc is far better (to my ears) for music than the Beam in a larger space.

An Arc and the mini Sub should be good.

In a smaller space the Beam is pretty good but you need to be pretty close to it to get a really good stereo image. I have two, one for TV and music (split about 10% -90%) and at four feet away it is pretty good. The other is on a cabinet in the bath (music only) and in that small room proper stereo imaging isn’t really possible.