I just installed ubercart, the drupal store. Now registration can start:

• PayPal should work fine now, but you can also pay by check or bankwire.
• You can book each of the two days separately. After registration a receipt will be linked to your account.
• In case you are not yet registered on this site: don`t worry, when you buy a registration package your account will be set up automatically during checkout and you will be able to log in to it.