Looks like there was a short hash added at the end of the name of the AKS cluster created by Pulumi. Is that expected behaviour?

Yes: https://www.pulumi.com/docs/troubleshooting/faq/#why-do-resource-names-have-random-hex-character-suffixes

Ahh, and it can be adjusted on a per-resource basis, excellent! Thanks!

Yes most properties have a name property that you can explicitly set. We also have https://github.com/pulumi/pulumi/issues/1518 tracking work to add more support for configuring names.