I have adopted a mini australian shephard from the shelter. She is smart as a whip, loves to learn and loves treats. I've had her 5 days and only been training her 2 (she has been sick). She is picking up sit, down and c'mon easily. I'm curious as to how many tricks to teach at a time (unmastered tricks, review on learned ones is always good). how many is too many? I'm sure is varies by dog but what's a good rule of thumb?