I'm sure that you have some rabbit recipes that you like - any seasonings that go well with other preparations of rabbit will go well with rabbit sausage. Maybe parsley, rosemary, sage, bay leaf, lemon-grass, coriander, or basil, in some combination.
Never hurts to start with a base of SPOG (Salt, Pepper, Onions, Garlic) (the latter in powdered form, typically). For five pounds of meat, I'd recommend 60 grams salt, and 50 grams each of the other three. If you make up a large batch of SPOG, you can start light, mix it up and make a taste patty.