The hazelnuts will be an absolute bollocks unless you can get ones that have already been shelled. No pun intended but they are a tough nut to crack. You might be better off using a hazelnut extract but that can also be problematic (extract or essence? What quantity?). But shelling hundreds of grams of hazelnuts won't be fun, trust me!
Other than that, this won't be much different to other stouts you have brewed. You'll be adding lactose towards the end of the boil, I imagine.