If you're casting a foretold card from exile for its foretell cost, you can't choose to cast it for any other alternative costs. You can, however, pay additional costs, such as kicker costs. If the card has any mandatory additional costs, those must be paid to cast the spell.

If Glorious Protector leaves the battlefield before its triggered ability resolves, no creatures will be exiled.

Casting a foretold card from exile follows the timing rules for that card. If you foretell an instant card, you can cast it as soon as the next player's turn. In most cases, if you foretell a card that isn't an instant (or doesn't have flash), you'll have to wait until your next turn to cast it.

Auras attached to any exiled permanents will be put into their owners' graveyards. Any Equipment will become unattached and remain on the battlefield. Any counters on the exiled permanents will cease to exist. When the cards return to the battlefield, they will be new objects with no connection to the cards that were exiled.

If a token is exiled this way, it will cease to exist and won't return to the battlefield.

Glorious Protector's enters-the-battlefield ability doesn't target any creatures. You choose which non-Angel creatures to exile, if any, as that ability resolves.

Because exiling a card with foretell from your hand is a special action, you can do so any time you have priority during your turn, including in response to spells and abilities. Once you announce you're taking the action, no other player can respond by trying to remove the card from your hand.