1. For the email message, we don't say that the administrator must activate the account. Maybe the translation in your language is not correct ? Here is the message of the email by default in english:
ACCOUNT_MUST_BE_ACTIVATED="Your account must be activated by clicking on the link below and you will be able to continue your order."
2. When the system is configured to ask for activation, once you entered your information and clicked on register on the checkout page, it just displays a message telling the user to click on the link in the email. Then, when the user click on the email, he will be redirected to the checkout in order to continue his order. I tried it on your website and it works OK.