Dark Chocolate Brown Recipe Critique

I brewed up what was intended to be a black beer that tasted closer to an amber, which ended up more like a porter after it finally all melded together. But just prior to that, for about a week, it had a nice dark chocolate taste, which gave me the desire to create a brown that had a nice strong dark chocolate flavor.

I'm uncertain as to how much chocolate (I'll be buying my grains from Austin Homebrew Supply as I live in Lakeway now so I'm not sure if there chocolate will be similar to the Briess I had been buying in San Antonio) I ought to use without getting into a more roasty flavor.

Here's my 6 gal partial mash/partial boil recipe:

5 lbs golden light LME (FO)
3 lbs 2-row
0.75 lb crystal 60
0.75 lb crystal 120
0.5 lb chocolate
0.5 lb soft white wheat berries
6 oz carafoam
1.2 oz Liberty (4.9%) @ 60 mins
1.4 oz Liberty @ 20/5 mins
US-05

1.055/1.011
5.7% ABV
32 IBU's
23 SRM

Sounds good... I'm seeing this beer as a maltier/chocolatey English beer. If it were me, I'd go Marris otter and an English ale yeast and keep everything else. I usually simplify the caramel malts, like 1lb of 90 or something and see what the color is supposed to be. If it's lighter, just bump the choco a bit. If you see it with a bit of an English feel like I do, maybe go fuggles for aroma?

I placed my order the other day.

I like using 2 types of crystal malts for what I figure to be a little more complexity.

How much chocolate can be used in 6 gals before it becomes roasty?