Thanks so much for your advice guys! I will try the squeaking for small nips and the scruffing for biting. I'm hoping this guy will settle down... One of the three is very friendly and non aggressive... If I do breed, it'll probably be from him (although he is doing some sneezing which is concerning). The third rat is shy, but is coming around with handling and treats.

It'll be challenging if I do decide to breed as there are no stores that sell females in my town... i may have to go a couple towns over to find some, but I'll worry about that when the time comes.

So far I am liking these guys' intelligence a lot (although they've proven quite the little escape artists so far).

Thanks again for your advice!