Hi Chance - this is a great topic, so glad you have started this thread, and best wishes for your backyard nursery goals!
Regarding specialty areas... one of mine is medicinary herbs. Many do not have straightforward propagation (or even clearly understood needs for propagation), and there are real concerns about depletion due to wildcraft harvesting. For some of these to be sustainable, we just gotta become capable of a farmed production base. (You can see more about the at-risk species here:
https://unitedplantsavers.org/species-at-risk-list/)
To this end, I can recommend this book by
Richo and Sena Cech: 'Growing At-Risk Medicinal Herbs'. Richo Cech is all in on herb seed saving and production, propagation, creating appropriate environments for herbs, etc. I have tied in one of his YouTube interviews below.
Carefully written, based on practical experience, and I am finding some successes with the guidance here that I would never have come up with on my own. This is the most specialized in
Richo's full series of books on plant medicine. All of them are good, though this one on the hard to cultivate at-risk herbs really provides an invaluable service with info I have not seen anywhere else.
If you are interested in having medicinal herbs as part of your future backyard nursery, these might want a place on your growing bookshelf.