*beams* I think you got every single little point I wanted to get across, which makes me awfully happy! Thank you!
My main theme was miscommunication, having Harry and Snape love each other but experience a lot of difficulty in getting things across, which would make the addition of Draco smooth their own relationship. I figured Harry and Draco are contemporaries and probably have a lot of little cultural things in common, but Snape and Draco are both Slytherins, both sneaky and cut from the same cloth. I liked the idea of Draco sort of being able to mentally adjust to each of them--and in much the same way many people in high society are used to making pleasant small talk and playing host, he'd be good at steering them, conversationally speaking.
It felt like they'd work well together because Draco's spoiled, but not with affection, and I could easily see Snape being greedy and not being TOO insecure he'd lose Potter to Draco--more see it as him owning both of them, which is, as you noted, a bit of a wink-wink on my part because the bottoms are really the ones in charge. And of course, the story was mostly about Harry coming to terms with the idea and realizing having Draco wouldn't have to mean that he and Snape meant nothing.
*laughs* I wanted a really absurd number of kids, just to underline how thoroughly whipped Severus really is.
It might be fun to do a follow up fic someday, just to include Lucius. I think he'd add some fabulous power-dynamics and control issues to the core family, don't you?