Personally I wouldn't go any smaller than 6" for bench stones. I see a lot of recommendations for tiny little stones. I think you are limiting yourself if you use such small stones. Some people can definitely do a good job with small stones. I don't think most people will produce very good results with stones smaller than 6 inches and really I think 6 is too small if you are sharpening any knives 8" or longer.
The Atomas seem like *great* stones. Had I known about them before I bought my DiaSharps, I probably would have bought at least the Atoma 140.
My DMT progression is based on something I read from a former BF member. His progression (and mine) is: XXC, C, EF. In practice this works very well and seems to erase the scratch pattern of the previous stone without too much extra effort. The XXC is worth a special mention. A stone with this kind of grinding power allows you to do things you can't with other stones. Fairly major tip repairs happen pretty quickly. Reprofiles or rebeveling damaged blades happen pretty quickly.
The XXC helped transform my sharpening because it's such a fast grinding stone. It finally became fast and obvious what I was doing on the stone. The cycle of: grind, observe, adjust, and grind again, became SO MUCH FASTER than before. Plus, it grinds so fast that I think it actually lets you make more consistent bevels. There's less time for fatigue to set in and less time for you to screw up the angle. See, as you grind a bevel, you are making it flat. Before it's nice and flat, your job is harder: Holding the blade at the same angle stroke after stroke. Once the bevel flattens out, it's easier because there's more bevel touching the stone. The XXC gets you to this "easy part" much faster. I hope that makes sense.
I haven't used the DuoSharps, but they have a lot of fans here on BF, Youtube, etc. I'm sure they work just fine. If you're serious about sharpening, I suggest you expand the budget a little and get 8" or 10" DMTs. I think the DuoSharps are kind of a bargain since they have two sides. But again, that XXC is SUCH a great stone and it's only available as a DiaSharp.
Good luck,
Brian.