Yes, it can be used after a wash to add gloss and protection. In fact, CB can be used as a stand alone sealant, similar to HGG, and is silica-based (vs HGG which is an acrylic resins). See the instructions on the bottle for application methods following a wash, etc. It's advertised for last months, but I can't attest to that since I use/favor HGG. I'd say using it once/month or so would be more than sufficient and any more often overkill, potentially losing some gloss, etc, because of too much with layering.
WW is awesome, and if you haven't done a wash using it, I recommend you give it a try. You might be surprised. And it smells incredible...addicting, even. Other uses are door jams and the engine bay. Compared to DS, direct from the product website, it "is a more effective cleaner, and has more lubricant designed to remove larger dirt particles without causing swirls. It also has no gloss enhancers, so it leaves your paint clean but not glossy. Follow Adam's Waterless Car Wash with Adam's Detail Spray to enhance the gloss!"