Membership and How to create simple sign up based on email address and user name only

We have installed membership plug in for our multi-site.

My goal is to allow our potential new users to sign up based on by creating a user name and providing a valid email address..

Can they become a member with this basic info and without sending them to paypal..

2nd or could you suggest another plugin to react with auto responder to this simple basic info and then tie back into membership once our new user is more engaged and ready to pay…?