Hi Jonna,
You probably already know about the Seed Identification, and Germinating Now threads on the SRGC forum, and the Seed Starting Chronicles on the NARGS forum.
When Kristl Walek(you may also know her from the SRGC) comes out with her book, maybe in the next year or two, I think it will be the very best of all for someone like you. But it will be perhaps a bit too involved for the general reader or many of your customers.