I used brown sugar when I bottled my oatmeal stout. Turned out decent enough(i also threw in fresh vanilla beans). I would be careful with the amount though, you dont want to over prime it.
As for the coffee, I have never done it. I would read up on read how much other people use. I think coffee generally goes into the secondary, and not the bottle though. That being said, go for it.
there is alot of experience on this forum, and i would generally trust the advice you get here, but never be afraid to experiment just a bit outside of other peoples advice and your own comfort zone.