Is this a subscription? Will I be charged again?
No — an event licence is a one-off payment for that event, with nothing recurring.
No. Upgrading an event is a one-off payment for that event. There is no recurring charge, nothing to cancel, and no renewal date.
Creating an account and creating events costs nothing; you pay only when you choose to upgrade a particular event.
Current prices are on the pricing page, and the Refunds and Cancellation Policy sets out your cancellation rights.