I use mostly oak on things, but occasionally I will do cherry or some hickory with a little pecan.
For the fattie I have a few favorites.
One was simple, smoke a head of garlic not till mushy/roasted texture but to where it is still firm then chop it up and mix throughout your sausage, reform and poof-smoked garlic fattie.
Another favorite I did was to saute some peppers and onions then in the fattie was some cheddar cheese, the peppers and onions (jalapenos for some extra heat) then favorite BBQ sauce.
If you have access to a fresh olive/mozzarella bar I like to sometimes put marinated garlic, mushrooms, mozzarella and sun dried tomatoes in a fattie.
Pepper shooters (marinated cherry peppers stuffed with aged provolone wrapped in proscuitto, wrap them in sausage and you have a delicious appetizer fit for a King.