One of the first BW's I made had some English dark malt in it, after reading the style guidelines I decided to go toward the darker end of the range. It wasn't my favorite, so I'd be careful with the chocolate malt. They are fantastic on the paler side when made with almost 100% MO, or even better Optic, or Golden Promise. If you want to go American, Briess malt for the Bigfoot type of BW.
Crystal malt is fine in a BW. Put yourself in the shoes of the brewers and brew with what they had available, what were the ingredients available to them 200 years ago or more that made that style of beer survive and become a classic style? It's an English style adopted by Americans. For an English BW, use English ingredients. For an Am BW, use American ingredients.
I always go to the bjcp style guideline when developing a recipe, there's an ingredients section. Between that and the OG, color, and IBUs specs you should be able to work up a great barleywine recipe.
17 lb of base malt, a lb of crystal and you'll be at 1.090 or so. Sounds like barleywine to me! Keep some light DME on hand in case your mash doesn't go exactly as planned.
I was considering 17 lbs of base and 1 of mixed caramel & choc. Is this overkill? It's my 1st try at it, so I wanted to check. Also, how long to ferment... Month?