The Cherokee Syllabary: Writing the People's Perseverance, Ellen Cushman, U of Oklahoma Press (2011) would be my top recommendation. It certainly has a primary focus on the syllabary, which absolutely goes hand in hand with understanding the life of George Guess/Gist - the English name of Sequoyah, but the work also does a great job of explaining much of his life in a biographical sense. Dr Cushman is a senior professor of language so it comes as no surprise that where her interest and scholarship really shines in this work is within the analytical description and review of the language and syllabary. She is also a member of the Cherokee Nation and has even served as a Cherokee Nation Sequoyah Commissioner. I've also come across some interesting writeups in books not particularly about Sequoyah such as A. J. Langguth's Driven West in which he devotes a chapter to the Cherokee genius. I also seem to remember finding one in my local friendly used book store not long ago, I'll see if I can dig that up (I found too many thinks I wanted and sadly that one didn't make the final cut).