Hi Spyro.
Any size Whimzee works but you can give them fresher ones more often if you get the ones for small dogs. I don't know about nutritional benefits. You'll know if they should be replaced when they turn white/pale. It will be easy to tell. Some like them and some do not. I have 2 or 3 that do and 3 that do not. They don't get yucky. They stay dry. I don't see why you can't give them a milk bone as well. Some will just nibble occasionally. Penny chews hers quickly. None of my hamsters chew wood chews, though I keep them in their homes just in case. Dog biscuits and peanuts in a shell are the only things they all really eat (except Gizmo can't) that give their teeth a workout. But some do like the Whimzees so it's worth a try!