Yes - the Source image stack allows you to add up to 4 separate images that would be switched out at the different breakpoints (the BPs in Source are 600px, 900px and 1200px).
So, if you were wanting to use all 4 (and wanted to make sure that they were full width at all sizes then yes - you would want one the small one at least at 600px, the medium one at least 900px, the large one 1200px, the x-large one is for devices wider than 1200px so you would maybe add a 2000px (but if you are using in a max-width container as you say then you wouldn’t need the x-l).
If you wanted to supply retina images you would want to supply images double these widths.
The other option is just adding a single 1140px wide image into the small image and this single image will be used on all devices. This will work fine but of course you lose out on potential file size savings (for the web page visitor) / being able to use different images for different device sizes / different aspect ratios for different devices etc.
Hope this answers your question?