For metadata licenses (Pro and Enterprise), no. If you only need one metadata license of Gearset, then simply choose the type you need and whether to pay monthly or annually. The choice is yours.
Data deployment cannot be purchased separately. Your data add-on would be added to each Gearset metadata license purchased.
Data backup can be purchased separately, and is priced per standard Salesforce user.
Regardless of whether you pay monthly or annually, you can cancel at any point - there's no long-term lock in.