Membership Plugin - One off payment (joining fee structure) possible?

1. Is it possible to use the membership plugin to charge a one off fee?
2. Can you change the narative/label on the button from say , subsciption to something like join now or join today?

I want to take a one time fee and have members who join have access to certain areas of the site, if they wish to they can upgrade to other features if they do so choose, using the levels within the plugin.

Thanks