Cards you don't cast this way, including any exiled land cards, will remain in exile indefinitely.

You cast the cards exiled with Fevered Suspicion as it is resolving. If you choose not to cast them, you cannot cast them later.

If the card has in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.

You may cast the exiled cards in any order, not just the order they were exiled.

If you cast a spell “without paying its mana cost,” you can't choose to cast it for any alternative costs. You can, however, pay additional costs. If the card has any mandatory additional costs, you must pay those to cast the spell.