This is cool! There's a lot of bad (and by bad, I mean misaligned with modern voice science and science-informed pedagogy) on the internet, so it's nice to see a resource striving to organize some good information.

A couple recommendations I'd suggest exploring to be even better aligned with current understanding:

Current literature does not distinguish between head voice and falsetto. While "falsetto" often carries a connotation of breathiness, that is not inherent to the register. Both are referred to in literature as laryngial mode M2, in which the Cricothyroid muscle is dominant in shaping the vocal folds. In contrast, chest voice or M1 is Thyroarytenoid dominant. While that may be a bit in the weeds, I found wrapping my head around this very helpful in cutting through a lot of confusing language around head voice .

Use of these different registers changes across genre and voice type. Classical sopranos and mezzos use head voice in their upper range, while musical theatre sopranos and mezzos bring their chest voice up (i.e. belting). Meanwhile, tenors and basses typically use chest voice for their full range in both classical and musical theatre genres, with much more use of head voice in pop/contemporary genres.

One other suggestion is to more prominently feature SOVTs (semi occluded vocal tract exercises). You reference them in your warm up section (lip trills and straw phonation) but these are highly effective and evidence-based tools to develop efficient phonation.

Further, for anyone looking to learn to sing (and anyone can learn to sing!), there's no better resource than a voice teacher. Most teachers nowadays teach online as well as in person. A great place to start looking for a teacher is through NATS or ICVT.