Suggestions workflow user registration in form tool

I have build a wizard tool to calculate water use and warming cost in showers with nice graphs on the confirmation page.

I now study whats the best way to get people more involved by making in account with a personal page where several results of these tools can be shown.
Think Buddypress.

So first of all, whats in your opinion the best way to get people registrated?
With the I know its possible.

what works best out of a conversion point of view?

  1. Start with asking there email/username/password
  2. Or ask these in step 3
  3. ask just email and password? And later ask more questins.

Because there is no official demo video of /add-ons/user-registration/ Iam not sure if it can this:

  • already registered users dont see the -required- fields for registration.
  • make the registration in a way its leas intrusive and more user friendly.
  • choose for double opt-in or single opt-in? Can a user start the forms, the finish the form without checking email and confirming the email link for double opt-in?
  • other ways of confirmation?

All examples of live sites are welcome so i can study UX and best practices

nobody? is this not a normal usecase?