[Mechanics] Balancing spellbooks for divine casters (Pf1e)

[Icereach]

I'm designing a campaign where classes that previously prayed for divine spells instead have a spellbook to study from. They'll gain 2+[casting mod] spells at 1st then 2/ level after that. They'll also automatically gain spontaneous conversion spells as well as domain spells. They'll of course have the option of scribing scrolls to their books, as well.

I know this has almost certainly been attempted before. If there's a thread already on the pitfalls and problems, I would appreciate a point in the right direction. Otherwise, what could some of the unforseen consequences be?

-Spellbook vulnerability
-Less versatile clerics
-Reliance on Spellcraft to increase spells known (probably the biggest one)

A running list of rules changes can be found under Yallek by following the Icereach Gaming link in my signature.