Add One Click User Login and Register to Order Checkout

I want to add User Login and Registration step to our checkout. [login to view URL] If you Add 1 product to cart, then you can press Checkout. I want to add the user login and registration as very first step. I want to allow for customers to be able to submit orders as guest. So on this login/ register step, there must also be a link for users to click who do not want to create an account. Like, Proceed with checkout as Guest. If users register or login, then in our original 1st step, we no longer need them to enter the Name or Email. Instead it should just greet the user by his name, like Welcome, John America! Then for email field, it will show his usernames email account and previously saved Phone Number. All fields should have text option that says, "Change or Edit" if clicked then field is enabled for input to replace the saved value. The website is built on Wordpress. It's a multi network site. We don't use Woocommerce. Our order form is custom designed on php code.