Magic users and Magic

I have some thoughts on spellbooks, scrolls, and magic in general. These ideas are a mash-up from various sources, and my own thoughts on the subject. If I'm covering some old ground, please bear with me, I'm just trying to consolidate these ideas.

The driving force behind these ideas is my personal assumptions of how magic works in my campaigns. These house rules are designed to enforce the particular flavor I am attempting to achieve with magic and how it fits into the overall "experience" of being in the campaign setting.

Spellbooks and Scrolls

Only Magic users keep spellbooks. Cleric spells are more akin to divine abilities, rather than the written prayers implied in various iterations of the rules.
The spellbook may only contain a number of spells equal to the number the character may cast, plus one extra spell per level if the character's Intelligence is 15+.
Magic may not be cast directly from the spellbook. Spells must be prepared in order to be cast.
Scrolls may not be copied into spellbooks. Scrolls do not contain the necessary formula for preparing the spell. Scrolls essentially contain a prepared spell, along with a trigger.
The only ways to add spells to a spellbook are through copying from another spellbook and research. Remember, though, that a spellbook may only contain a limited number of spells (see above).

Casting

Spells may be "Readied", that is their casting almost complete, waiting only for their power to be loosed. Readied spells take effect earlier in the combat sequence than normal, occurring during the missile fire stage. Otherwise, the player must state the spell being cast during Declaration. Assuming the casting proceeds uninterrupted, such spells take effect on the character's initiative  point.