QIf I don't have any Wyrmkin followers in my cemetery, can I still discard a card as part of this follower's On Evolve ability?

ANo. You cannot select a target for the ability, so you cannot play it at all—cost included.

QWhen selecting a follower from my cemetery, can I select the card I discarded as part of the cost of this follower's ability?

ANo. You must select a card before paying the cost.