Buying a username almost always means buying the account that currently holds it — not a standalone "just the name" transfer, since usernames aren't detachable from their account on any major platform.
Whatever followers the account already has, yes — but follower count isn't guaranteed to stay stable and shouldn't be the main reason for the purchase.
Open the vault, pick a listed username, and DM the contact handle shown on the site to arrange payment — there's no cart/checkout, it's a direct conversation with the seller.
Crypto-only. See the Terms of Service for the full payment and delivery policy, including the sale-finality and 72-hour issue window.