Soulbright Seeker

If a cost to cast a spell includes revealing a card, that card remains revealed from the time the spell is announced until the time it leaves the stack.

You add {R}{R}{R}{R} only the third time Soulbright Seeker's last ability resolves in a turn. You won't get the bonus mana the fourth, fifth, sixth, or any subsequent times in the same turn.

If a card in your hand is already revealed (perhaps because it was revealed to pay a cost of a spell that's still on the stack or due to the effect of a card like Telepathy), you may reveal it again to pay the cost of another spell or ability that requires you to reveal a card from your hand.

Because it has a target, Soulbright Seeker's last ability is not a mana ability. It uses the stack and can be responded to.

If an effect refers to a "[subtype] card," it refers only to a card that has that subtype. For example, Glen Elendra's Answer creates a Faerie token and features a Faerie in its art, but it isn't a Faerie card.