I LOVE Jeff's work and I own his Ansible book. The setup is pretty awesome. FWIW I think you could do this with local VMs a little more easily and provision with Vagrant. Having said that, a cluster of Pis is super fun!
Yeah, using local vms is going to greatly expand access to this kind of learning. A current developer laptop is more than beefy enough, and I'd suggest that there aren't many useful lessons to learn from the pi hardware that can't be learned fully virtualized.
But if you're having fun, of course, more power to you :)