Can I sacrifice 5 creatures?
Sacrificing creatures here is part of the cost, so you can simply sacrifice five creatures (all at once) to pay for the ability.

Costs are always things that, if you're able to spend the resource in question or perform the action in question, you can do so to pay for the ability. If something has mana or energy as a cost, you can pay mana or energy for it. If a permanent has an ability with tapping as a cost, you can tap that permanent to pay it. If it requires you to discard cards, or exile cards from your graveyard, or sacrifice creatures as a cost, you can do so to pay it.

So no, you don't need anything separate, and in fact, you can't sacrifice the creatures for anything separate. They're the cost for this ability, and that cost has to be paid here, just like a mana cost would be - see Can I pay two different costs with the same payment?