A fistula is a track that is formed when an anal abscess pushes through the tissue as it makes it way to the surface. In the case of people with a jpouch, an anal fistula will either open up on the outside near the sphincter, or drain into the pouch itself. They can be difficult to deal with, as cutting into the anal sphincter can lead to incontinence, and they can sometimes come back.
Cuffitis is when the "cuff" of the rectum, the small piece they left after the colectomy becomes inflamed. The cuff is what connects the pouch to your anal muscles. Since this is still technically "colon" material, it can sometimes become inflamed the same way your colon did with UC. It's treated the same way as well, usually with a steroid suppository, which usually puts it into remission. People who have severe chronic cuffitis sometimes a pouch advancement surgery, which removes even more of the cuff, pretty much attaching the pouch as low as possible.