Stout Braggot? cool idea, I'm not an expert but I got my start in homebrewing making braggot. and I make two or three batches a year. first you gotta decide if you want a "BEERY braggot? or a "MEADY braggot" now you want to do stout so I'm guessing you'll fall on the beery side of things. for me a good rule of thumb is one of thirds. if ya want beery braggot a weight of honey that is about one third the weight of grain. this is not exact but until you get an idea of a SG from three or four lbs of honey its hard to know what your working with.
second is honey flavor control, I agree with the above posters that lighter beer styles work better for allowing the honey flavor to come through, so you might want to increase your honey to four lbs or so. I cant speak to what type of honey to use as i have access to either store bought or a local wild flower honey i use the latter for all my braggots and they are great. if all you have is store bought itll work just fine I have used it for my first batches with great success. sams club sometimes carries honey in bulk jars.
another thing to watch is fermentation temp, keep it on the low side or you might get some belgian funkiness that i'm not real fond of. the braggot is perfectly drinkable its just my taste. personally i like my braggots light, as in not chewy or cloying so I prefer a beery braggot. as to the stout question with all the dark grains to balance the sweetness you should be good but i might suggest reducing you crystal malts as you wont taste them anyway.
as an aside i just tapped a keg of "dark" braggot which is my standard recipe with a little black malt and roasted barley added to the grain bill. it turned out great but i think ill reduce the roasted barley and add more black malt next time to up the acidity a little. hope that helps and good luck.