Good luck! My little girl is working toward competing later this spring or in the summer. Chis can and do love agility. The only catch can be if they are heavy enough to tip the teeter. They do need to be about 5 lbs for that. I hope you find a good, positive reinforcement class to start in and have fun!!
Your dog does not have to be purebred to compete in USDAA or NADAC but does have to be with either papers or a PAL to compete in AKC (go to the AKC's website if you have questions).