How exciting! 
I am cheering you on in full force as you continue your journey into herbalism- it sounds like you’ve already got some great plans in place! 
In terms of a book of herbal spells, I just finished the Wicca Book of Herbal Spells by Lisa Chamberlain and I really enjoyed it. She recommends a “one herb at a time” approach, where each herb is studied and then a few spells with minimal ingredients (to put the focus herb in the spotlight) are explored. I really enjoyed it and recommend it to anyone studying herbal magick! 
For free herbal resources, there are a few here: Free Books for Green and Kitchen Witches 
Seconding Amaris here if I can- the @Mistress_Of_Herbs truly lives up to her username! 
Ohhhhh I was actually working on my own materia medica design a while back, but I never finished it (I wanted to do a separate version for mushrooms too… 
)
I really ought to finish it- thank you for the reminder (and inspiration), @Artemisia!
Wishing you all the best as you learn- keep on having fun with your herbal studies!