I'm happy to help out if I can. Those who know me here will hear me go on and on about the virtues of pre-Edo iron, especially Azuchi-Momoyama Owari tsuba... So again, if you'd like to set up a time to talk in live time, just let me know. I'm in San Diego, so on USA west coast time.
Just a thought or two to add quickly here. As concerns Tsuba: An Aesthetic Study, it was really the Introduction of the book that I found most rewarding, mostly because it confirmed/supported a viewpoint I'd long held: that it is the plate of the tsuba that matters first and foremost in a pieces's beauty, not any applied decoration, whether sukashi, carving, or inlay. The book is worth getting just to read this argument.
Next, another "small" book on Japanese aesthetics is Donald Richie's A Tractate on Japanese Aesthetics. It is all of 79 pages, but it introduces and explains many aesthetic terms/concepts that were in use from the earliest centuries of Japanese history, on through the Muromachi, Momoyama, and Edo periods.
The book Ford mentions, Tanizaki Jun'ichiro's In Praise of Shadows is one I not only echo in recommending, it's a book I quoted from rather liberally in an article I wrote on the importance of lighting in iron tsuba appreciation.
I would second Henry's comment that for text, Sasano's gold book is the one to have, but for images, his silver book is a must-have.
I should mention, too, that to really understand pre-Edo iron tsuba, you must also familiarize yourself with the Tea Ceremony and the articles used in that practice (the ceramics, in particular, for many of the aesthetic concerns attached to the Tea Ceremony (which was a hugely important cultural phenomenon of Momoyama and early Edo times) also informed the design and construction of upper-level iron guards. Contrary to what some might say, the finest of iron tsuba of those times were meant for high-ranking bushi, the same bushi who were also intimately involved with Tea.
Finally, it's worth noting, I think, that the most celebrated tsubako of all time for the Japanese (generally speaking, of course) are Nobuiye and Kaneie, both of whom worked almost exclusively in iron and were Momoyama artists. Many will argue that these tsubako best expressed many of the most valued aesthetic principles of their age (or any) age.
There is SO much more to say on this, Chris, so please do get in touch...