Multiclassing

Would a temporary stat bump fulfill a multiclass prerequisite, or does the base score have to meet the requirement?. Your base score, not a temporary score, has to meet a multiclassing prerequisite.

When multiclassing, do you get the cantrips from all your classes?. If any of your classes grants you cantrips, you get all of them.

Do you gain proficiency in more saving throws when multiclassing?. When you gain a level in a new class through multiclassing, you gain only the traits listed under the "As a Multiclass Character" section in the class's introduction. This does not include saving throws.

However, if a class grants additional proficiencies or training through one of its features, you also gain those, regardless if the class is your first. For example, if you gain a level in Cleric and choose the Protector option of the Divine Order feature, you gain proficiency with Martial weapons and training with Heavy armor, and if you're a Gloom Stalker Ranger and gain the Iron Mind feature, you gain proficiency with Wisdom saving throws—even if Cleric or Ranger respectively isn't your first class.

Can a Barbarian/Fighter (Battle Master) use maneuvers while raging?. Nothing in the Barbarian's Rage feature precludes the use of maneuvers.

Can a Rogue/Monk use Sneak Attack with Unarmed Strikes?. The Sneak Attack feature works with a weapon that has the Finesse or Ranged property. An Unarmed Strike isn't a weapon, so it doesn't qualify. In contrast, a Rogue/Monk can use Sneak Attack with a Monk weapon, such as a Shortsword or a Dagger, that has one of Sneak Attack's required properties.

A Wizard multiclasses into a Sorcerer with the Wild Magic Sorcery subclass. Do spells cast from their spellbook trigger Wild Magic Surge if they are on the Sorcerer spell list, or do they have to gain them from Sorcerer to trigger?. From the multiclassing rules: "Each spell you prepare is associated with one of your classes." This rule means only the spells prepared as part of your Sorcerer class features trigger Wild Magic Surge.