scottwaltner Good questions! First on the cure, if you are not going to smoke it I would not add any cure. It isn’t going to hurt anything but it isn’t needed. I would also not mix it as thoroughly as you would if you were going to smoke it, leave it more like a bratwurst texture.
If you are going to use pork butt then I would recommend you go 50/50 depending on how fatty your goose is, some of them can have a surprising amount of fat but generally they are somewhere in the 10% so 50/50 with pork butt will be ok. If you are going to use straight pork then I would say about 20% pork fat. Remember to mix either the pork butt or fat during the grinding process.
One other thing I would recommend is you use a binder like Sure Gel or Super Bind or if you dont want to use one of those then Carrot Fiber works really well to increase the water holding capacity of your meat. If you try this and still find it too dry then I would recommend looking at this post for seeing how using Cold Phosphate can help https://meatgistics.waltonsinc.com/topic/415/how-to-make-a-juicy-homemade-turkey-bratwurst
Good luck and as always we want to see pics!