Material spell components are consumed/destroyed/expended when the spell is cast, unless specifically noted otherwise (PHB p. 113-114)
Priest holy symbols are not lost when a spell is cast (PHB p. 114)
Touch-delivered spells uses the best available THAC0, so a fighter/mage can use their fighter THAC0 (Sage Advice #203 p. 89).
Touch-delivered spells against the targets normal armor class, including adjustments for armor worn (Sage Advice #232 p. 93). If the Player's Option: Spells & Magic rules are used, some spells ignore the armor of the target, but the armor magical bonuses still apply. (PO: S&M p. 120)
Spell Books & Learning new spellsSpell Books
A spell requires its level plus 0–5 (1d6-1) additional pages (DMG p. 63)
One spell book page cost 50 GP (DMG p. 63)
Maximum spell book sizes: Standard 100 pages; Traveling 50 pages; Scrolls 25 pages (DMG p. 63)
A wizard can never have a spell in his book that he does not know (PHB p. 107)
Learning new spells
It is up to the DM if read magic is needed to read captured spell books
Wizards do not need to cast read magic to decipher a captured spell books. The language of magic is a universal language. (Sage Advice #175 p. 77)
Once a character has studied a spell book or a scroll with read magic spell, he or she will understand the new spell's general effects and limitations. (Sage Advice #263 p. 26)
Wizard scrolls require a read magic spell to decipher (PHB p. 144)
A wizard cannot learn a spell that is higher level than he can cast (PHB p. 107)
A check is made to see if a spell can be learned. If it fails, another check can be made after the wizard advances to the next level (provided the wizard still has access to the spell) (PHB p. 22)
Both versions of a reversible spell is recorded in the wizard's spell book (PHB p. 168)
Standard time required to add a spell to a spell book: one to two days per spell level of spell being entered (DMG p. 62)
Learning from Scrolls (Scroll Research)
The time and cost required is halved (DMG p. 61)
Scroll Research can never be done in an adventuring situation. The wizard must have carefully controlled conditions to even attempt it. (DMG p. 61)
Regardless of success or failure of the research, the scroll is destroyed. (DMG p. 61)