Playing with pro-sites sign up, going to:
Then I have the option:
Signup on Checkout
Disables WordPress Signup
Then when not logged in and visiting:
I choose a package reviewing the username, password, email, site title, site address fields.
I fill those out select "Reserve your site" and green check boxes show up next to the site title site address.
The stripe credit card info does not show up. If I then choose a different package, then the credit card info shows up.