kjm, can you stick a small silt pond above the larger tank to catch incoming sediment there?
I would advise running a waterline through/around the dam to a point below it, which will allow you to water the cattle in a tank (trough) rather than in the pond (tank). I do this at both of my ponds (tanks); it eliminates all the wear and tear on the shorelines by the cows. If your climate is so hot that they need a wallow in the Summer, I understand.
You don't have to feed catfish, although they of course grow much faster if you do. A stocking of FHM would provide non-fed catfish with a foodchain.
Lastly, your idea of porcelain structure is brilliant! (My next pond will have a bathtub in it.) One word of caution on those toilets - remove the flush levers. That is one place that a lure could snag on and, if you happened to pull it just right and it stuck in the open position, could cause the pond to drain through the bowl.
