Need Help with a partial mash 2 gallon batch..

Making, hopefully, a stout. Ingredients are..

1lb Chocolate Malt
1lb Black Malt
1lb Roast Barley
3.15lbs Gold Extract
1oz Magnum Hops
1oz Brewers Gold
Nottingham Yeast

I get the idea of the process but doing a 2 gallon batch it's hard to find correct data.

What temperature should I mash at?
How much water should I mash with?

I also want to include some oats into the recipe

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.

You'll want to cut out the black malt entirely, use 1/2 to 2/3 lb each of chocolate malt and roasted barley, add some 6-row for conversion (amound to be determined by how many lbs of oats you mash, stick to about equal weight as or slightly more than your other grains)

Mash at ~152 for 45 minutes or so with 1.25-1.5 qts water per pound of grain.

I did get the recipe idea from an imperial stout so I guess it might turn out to be an imperial which is fine, although I want to have a defined chocolate flavor in it..

So save the black malt for another recipe?

How do I incorporate the oats in the recipe?

To get a seriously distinct chocolate flavor in a recipe of this magnitude, you might need to use some actual chocolate . I haven't toyed with an imperial chocolate stout myself, so perhaps someone else can speak to that.

I'd say you should be able to just toss 8-12oz of oats in with the remaining grain bill for mashing. However, as I recall you need to mash a base malt in with them for proper utilization; perhaps throw 1lb of 2-row in alongside to compensate?