Gathbard
I've seen other games lock in the buff to the hotbar, and I kinda dislike it there, as the buffs can be placed on others so it can feel kinda bad to be the "buff bot" at times, when we are already working with limited bar space. I think casting from the book is probably the best option, but I assume that functionality would take a while to develop and get working correctly.
(can you cast ANY spell from the book? or just "buffs" how do we classify that)
a seperate bar seems like it could also work but what would the real purpose be in that vs just casting from the book? would you only be allowed a few buffs in this new "buff bar"? making you have to chose between those options only?
alternatively we could make most buffs into simple auras, and that would free up hotbar space and clean up the tedium of swapping spell slots for buffs, but it would also make it so that you'd never be able to buff a fellow traveling player, or give someone a SOW (or other sought after buffs.
overall i think casting from the book is probably the best of these solutions, maybe add extra cast time for spells cast from the book to make up for the time saved from not memorizing the spell. (this would also discourage casting more combat related spells from your book instead of your spell / ability bar)
Side note: I really would like to see some organizational features added to the spellbook, things like bookmarks, notes, Being able to create my own spell "Tabs" would be very welcomed.