The Arc is the best device for Home Theater use, I’d get it with a Sub or two, and a set of Sonos One SLs for surrounds. 

Note that Sonos does not have the capability for three separate front speakers, they’re all built in to the Arc, nor do the have disparate Atmos speakers, they’re also inside the Arc. 

Can I use just the arc?  Will that work with a TV?

Sure. You’d still get the three front channels, and the Atmos upward firing speakers on an Atmos signal.

You can add the ‘theater’ aspect of surrounds and a sub later.