I would like to customize the checkout page with a "continue" button under email that will enables the shipping information. The purpose is to get the users to give their email before they can enter other information , so when a user enters email and press "continue" the shipping fields are enabled and shown below.
Well, you have to use jQuery for that,
Simply remove all unnecessary fields & display Email field only at checkout then hide 'Next Step' button and add separate 'Continue' button beside that.
So, whenever the user clicks on 'Next Step' button after entering an Email, he or she can proceed to check out process.