1) the class for the span tag should be:
The ID is not important as long as it is unique.
2) When adding the email address validation, you can select the option to Allow Blank Entry. This way the invalid email address error will not display if the email address is left blank.
by also adding the required validation, it will force the email address to be a required field that cannot be left blank, regardless of the Allow Blank Entry setting in the Email Address validation
3) All form processing (this includes server validation) must occur on the forms action page. In the tutorial, they are validating the checkout form on the checkout page. The action of the checkout form is to post to the confirm page, all of the processing of the checkout form must occur on the confirm page in that instance.