For Seasonings and casings, Hi Mountain has several different types of sausage kits available on their website and through dealers such as Cabela's and Scheels, as well as some local retailers like myself (I only stock the Summer Sausage kit right now though). Once experimentation kicks in, the cheapest I've found casing (haven't looked very hard) is Allied Kenko, they have a website with a ton of stuff for sausage making.
For grinding, I think the KitchenAid attachment should work fine, but based on my experience with my new 1/2 hp grinder/stuffer, the stuffing attachment would be disappointing. I tried a batch a couple of weeks ago, and while the grinder performed beautifully during the grinding, it was very frustrating to use during stuffing...so bad that the next morning I ordered a 3 pound lever style stuffer from Cabela's ($69.99 I believe).