I've always been surprised by the amount of bourbon that Denny says he uses in his BVIP. There are other threads if you search for them.
I don't think I've ever added more than 8 oz. of bourbon to a 5 gallon batch.
I recently had a BBQ where we tapped my bourbon porter and it was pretty sweet. I think it had aged for maybe 8 months or so. Maybe longer. Bourbon will add sweetness to the beer, so that is something to consider.