Doing some quick calcs with Beersmith, that's a hell of a lot of sugar for a 2 gallon batch; I get about 1.086OG. Are you shooting for an imperial stout here? Do you want a dry stout?
If you're shooting for drier, which it looks like you probably are, lower mash temp should serve you better. I'd shoot somewhere around 150F-152F for at least 45 minutes; Beersmith says 3.75 quarts of water for the initial mash for a single infusion.
That said, I don't know that you need both chocolate and black malts in there. I'd stick with just chocolate, especially if you're bringing oats into the equation as well. The black malt will bring in some serious roastiness that, when combined with the barley and chocolate, could very quickly overwhelm anything else in the profile.