What's the best way to collect names and emails for a beta?

Hello, I'd like to collect names and emails for a week or two before inviting those people to sign up for an account on my new MU setup. What is the best way to do that? Should I use the Mailchimp integration plugin that syncs users with MC or should I just have a vanilla MC signup form? Is there an advantage to having beta people sign up as an actual user before creating their site? For example, would it be easy to create a site for an existing user without them having to signup again?

So. Many. Questions. Thanks in advance!