Well, not really. It all depends on your application. Needless to say, low polys perform better, high polys looks better. Number of polygons also depends on how many of animated models you will use simultaneously. It also depends on background scene. A few hundreds polygons may be optimal, but again it depends on your application.
Number of bones in skeleton does not make much difference. It certainly increases memory usage and processing but not that much. No other requirements for bones in skeleton.