frothdaddy - From what I have read, 2 beans seems to be standard. Apparently using 1 vanilla bean does not contribute much flavor-wise. However, I have no personal experience as to how many beans to use.
Based on the comments above, I have decided to make some adjustments to the recipe. First off, I plan on cutting out the cocoa, vanilla, and lactose entirely. I would like to get a decent base stout before trying to be clever with flavorings. Second, I plan to add in the 3 lbs of white sorghum syrup at flameout instead of at the beginning of the boil. Third, I plan on adding the oats to the 24 hour chestnut mash (though I don't think there will be too much conversion here as I don't plan on employing a glucanase rest). The last concern I had was whether I need more fermentables or not. The original Trails End chestnut beer recipe (http://www.chestnuttrails.com/pages/chestnut-beer) calls for 5 pounds of corn sugar to be added after the chestnut mash. Right now, I am just adding 3 pounds of sorghum syrup and 1 pound of dark candi syrup which will provide much less fermentables than that. I was thinking of adding an extra 1.5 pounds of sorghum syrup or maybe instead 1-2 pounds of rice syrup solids at the beginning of the boil. Another option would be to add more dark candi syrup, but I think that might be quite overwhelming especially with the 7 pounds of roasted grains I am using. Any thoughts?