#turn structure

fire lord azula allows you to copy spells while she's attacking. can you copy spells after damage but still during combat?

yes! you can! if we gave her first strike, we would be able to copy after first strike damage, but before regular damage, right? and generally things work similarly with or without first strike. which is a bit of intuition behind this ruling. (if first strikers were removed from combat after they first strike, then giving them double strike after first strike damage wouldn't work how people would expect it to.)

Yes.

When a player’s upkeep step begins, first any triggered abilities that triggered when the step began are put on the stack and then players get priority starting with the player whose turn it is.

The mana pool empties at the end of each step and each phase.

Whenever a step or phase begins, any turn-based actions for that step or phase happen first. e.g. you draw a card in your draw step. After these turn-based actions happen, any triggered abilities that trigger at the beginning of that step or phase will trigger. These triggers will then go on the stack before players receive priority. (Unless it’s the untap step, where no one ever gets priority, or the cleanup step where no one gets priority unless something triggers from the cleanup actions.)

So for Teferi’s Puzzlebox, you’ll first draw normally for your turn and then Puzzle Box’s trigger will go on the stack and resolve.

No.

Players don’t receive priority in the untap step ever.

The earliest in a turn that you can cast Glorious End is the upkeep step, so your opponent will have had the opportunity to untap their lands and can cast a instants or spells with flash in response to Glorious End.