Do I need a credit card to sign up?

Yes, you need a valid credit card. In order to start the 7 days free tial you do not need credit card. Only after the 7 days trial period expires, you will be charged on a monthly base according the price plan you have choose and then you will need a valid credit card so you can go though the payment process with PayPal.

You can also choose not to go through the 7 days free trial and go directly to the Subscription.  In that case a valid credit card is required and you will be charged once you confirm this from your PayPal account.