I don't know how much space the RO takes, but everything else should fit with space left over. Are you going to have a soap dispenser? If so, with all that in there, I'd also allow a bit of room for a soap bottle and the Never MT if you can. If not, definitely use a top fill bottle. Also think about other cleaning supplies or tools you might want at the sink. I put in a tilt out for those, but it does push the sink further from the edge.

Under the counter, you should have plenty of room for all of this stuff, but accessing it to change filters / adjust temps may be difficult if the sink is too small. Up top, it may look a little crowded. If you find it to be tight, make sure your filter is easily reachable from the front (ie mount it on a side wall, not the back)

Here's ours in the butler's pantry. 33' double bowl sink, with the instahot, filtered, and faucet.

Looking at the picture, I can imagine having the filtered water disp on the far right corner, and shaving off some space in between... it would probably be fine.

Thanks for your photos and replies. Yes, we want the soap dispenser also. That's why we want ONE faucet for the instant hot and filtered water. That would be at least three "things" in total on the counter behind the prep sink: one faucet for instant hot and filtered water, one regular faucet, and one soap dispenser. Maybe four...disposal air switch as well? I was thinking of an undermount prep sink that is about 15" by 15" inside. I think it will work on the counter; I'm more concerned about underneath. I figure the rest of the cleaning supplies will be under the main clean-up sink and the dishwasher air gap will be there, too. Maybe I need to just buy all of the products ahead of time and see how it fits.