I use the KA grinder attachment as well, and it does an excellent job. I opted to go that way based on the recommendation in Michael Ruhlman and Brian Polcyn's excellent new book "Charcuterie," which anyone interested in making sausage at home should have. They advise nearly freezing the meat before you grind it to avoid "smearing" - I did that and it worked perfectly.
I use a dedicated stuffer, one of the vertical screw-operated press models sold by a number of suppliers of sausage making supplies (mine came from The Sausage Maker). I find it much easier to use than making the grinder do double-duty, but it's admittedly a considerable extra expense that may not be worth it for you.
I've been getting my casings and other supplies from Butcher & Packer and am very satisfied with their quality and pricing. The hardest part of the whole operation was finding a good source of fatback, which I now get directly from a small abattoir in our area west of Boston.
I have the grinder and stuffer for the KA mixer. For small batches and the few times I've used it, it works fine. If you're going to get more into it, you should look into separate grinders and stuffers. I get casings from Allied Kenco, and they carry a variety (up to commercial scale) of equipment.