If a spell that's copied is modal (that is, it says "Choose one —" or the like), the copy will have the same mode or modes. You can't choose different ones.

You can't choose to pay any additional costs for a copied spell. However, effects based on any additional costs that were paid for the original spell are copied as though those same costs were paid for the copy too.

If you copy multiple spells with Display of Power, you can put the copies on the stack in any order.

If a spell has damage divided as it was put onto the stack, the division can't be changed, although the targets receiving that damage still can. The same is true of spells that distribute counters to targets.

The copies will have the same targets as the spells they're copying unless you choose new ones. You may change any number of the targets, including all of them or none of them. The new targets must be legal. If, for any target, you can't choose a new legal target, then it remains unchanged (even if the current target is illegal).

If you cast Display of Power, you can, at most, make one copy of each instant and sorcery spell on the stack. It's not possible for one Display of Power to copy the same spell multiple times.

The copies are created on the stack, so it's not "cast." Creating the copies won't cause abilities that trigger when a player casts a spell to trigger.

Any choices made as a spell resolves won't have been made yet once it's copied. Any such choices will be made separately as the copy resolves.

Display of Power's first ability only functions on the stack. It can still be copied from your graveyard, your hand, or any other zone.

If a spell that's copied has an X whose value was determined as it was cast, the copy has the same value of X.