Aussies are the shizz! There's a red merle male in my agility class and he's such a character also should be getting mine in a few years not to sure when now though since I decided to wait instead of getting mine this fall.
With my two for mental stimulation we generally just have a few short training sessions a day. Abby works on her HW for agility as well as obedience and some new fun tricks and Bo well right now we're working a lot on his skills with other dogs and his reactivity.
Puzzle toys are a great idea. I have
this one Bo has mastered it, but Abby is to smart for her own good. She'll sniff it then just sit there and stare at me because she knows if she waits long enough I'll given in and give the treats to her. And if I walk away she'll just ignore it then let Bo get at it and steal the treats from him when he gets the thingy out.
Other treat toys like kongs and toys like the hide and squeak squirrel toys are also good ideas...
Also as far as agility training you can work on foundation training and uprights when you have time that way when/if you decided tog et intoa gility and take classes you've already got some work done
for example
this- their working on the basics like hand touches, targeting, etc. Also start line stays are a big one
and
this- working her pup on uprights