I think you are on the right track--keep up the search to learn what works best for your specific situation. Just like people, each Aussie has an individual temperament, some reserved, some outgoing, some laid back, some high energy-you were blessed with the eager to learn, 'easy' one the first time. It did make me chuckle when I read what you wrote:
We are planning to neuter him within the next couple of months. The vet said that his broken tooth may come out on its own, or need to be dug out. So we are waiting to see if that happens soon, and if not he will be neutered and have his tooth taken care of at the same time, so he only gets the anesthesia once.
Poor guy...goes in to the vets office, clueless...comes out a short time later missing not only some 'hardware' but a tooth! Reminds me of the time I took a stray cat in to have him neutered only to pick him up later that day and talk to a very sheepish vet--they too 'assumed' he was intact, and it wasn't until they put him out and began the surgery they discovered he'd already been neutered, just appeared as if he was still 'fully loaded.' Poor Rex...he probably wished he hadn't stopped at our house, that may have been why he ran off from his first home?
Anyways--neutering asap would be a very wise idea. And as others have said, find him a 'job' to do in addition to basic (and advanced) obedience training--it could be formal, such as agility, flyball, work with a herd dog trainer...or just grab a tennis ball and a baseball bat every day--whack that ball, or frisbee, or jollyball, whiffleball...hide-n-seek...a busy mind is a good thing for a smart Aussie, or any breed. I hate to hear folks stereotyping Aussies in a single category as aggressive, very sad that that is the only experience they have had with them.