A teifling takes fire damage and has Armor of Agathys does it take the resistance to fire from the teifling?

Any advice on what school of magic to prescribe for enchanted/magic items upon casting Detect Magic?

Bonus actions: if a feature says you can do X as a bonus action if you do Y, you must do Y before you can do X

Great Weapon Fighting + Battlemaster’ Sweeping Attack: may I reroll the 1 and 2 of the superiority die?

So if you’re a Cleric > Wizard, you do not benefit from Wizard ritual casting?

Can undead attune to magic items, being that they’ve “died”?