A few membership questions (Free user, registration, styling)

Hi, I'm using latest version of Membership and I'm in Sandbox mode.

Here is my membership registration page
1. I'd like to know why the Visitor membership does not include a way for someone to sign up. If it's because the default access level for site visitors is set to Visitor, then how do how I remove this membership as an visible option?

2. I don't have any registered users on my site and I'm unfamiliar with WP registration set-up. I created a test user with Membership and noticed that the confirmation email was sent from a non-descript mailbox on my server, not from my site name. How to fix that?

3. Styling.. are the sign-up buttons supposed to look the way the do? Is there a way to make them look more normal, so the whole button can be seen? Buttons from other WPMU plugins seem to appear fine in this WPMU theme.