New Email Account creation and transfer?

I've like to change my email address on the primary user by adding a new email address while keeping my old one still intact.   Slowly converting all my accounts and contacts  over to my new email, while still monitoring my old email account.  Then eventually transferring everything I want to keep from my old email into my new one and deleting the old and having the primary user account my new email /username. How do I go about doing that on Xfinity website without messing everything up. 

 I think it will probably take about 2 months to get everything and everyone switched over to my new email address, since my old email has been the same for about 20 years.