This is similar to what I have in secondary right now. My recipe was:
6.6 lbs Amber extract
1.5 lbs Crystal 80
1.0 lbs flaked oats
0.5 lbs chocolate malt
0.5 lbs roasted barley
10 ounces lactose
8 ounces unsweetened cocoa powder
Wyeast Irish Ale Yeast
It tasted pretty good transferring to secondary, the dominating flavors were chocolate (obviously) and coffee. The chocolate wasn't overdone but added a really interesting complex bitterness.
The lactose I added to help balance out the bitterness of all that cocoa, and it helps make a nice body. I'm thinking at bottling time I'll add a few more ounces of lactose as it's still a little bitter. I'm contemplating adding some chocolate liquor and vanilla extract at bottling time.
I'd suggest that when you're ready to bottle/keg, take a few samples and play with them. Add a bit of lactose to a sample and see if you like it better.