VTRK (https://github.com/thestonefox/VRTK) will almost certainly make your life better. It's (well done) implementations of (most? all?) the core AR/VR interaction patterns that have been worked out so far.

I might go so far as to say it's the ActiveRecord to Unity-as-Rails for AR/VR, although the analogy is really flawed.

While I like your overall approach (a true, comprehensive intro to Unity), I would have liked to see more about, I guess I'd call it, the philosophy of putting code into Unity, covering (specifically and, IMHO, most importantly) the type of component system they're using, and type of event system they're using. The equivalent of describing a new language in terms of which features from the language grab-bag the authors decided to use.

PS - Pluuuuug, because dealing with JSON/YAML in C# suuuuucked: https://github.com/narfanator/maptionary