A regular sized cat litterbox is WAY too small. We found the 3x5 showerpan to be barely big enough. A small plastic kids wading pool can work as a litterbox too so long as the sides aren't too high for them to easily get in and out. They may eat a few pellets at first to taste them, but there's really no worry about them eating a lot of pellets. The pellets are just pine, non-toxic, and will pass right through.
Get a large, heavy no-tip water bowl from the pet store. Biggest, heaviest one you can find.