Adding a new email is pretty easy to do. Just follow the directions here: https://www.xfinity.com/support/articles/adding-new-user-names-or-email-addresses
You can delete any email account EXCEPT for the primary user account, which will allow you to sign in to all things Comcast and view/pay the bill.
To delete the ones you don't want
Sign in to Customer Central as the PRIMARY user account.
Users & Settings tab.
Click the drop down arrow next to the name that shows in
Choose the account you want to delete.
Then click Suspend/delete account under Account Settings.
Follow the prompts to complete the deletion process.
If you want to delete the primary account you will have to convert a secondary account to the primary.
To do this follow the instructions here:
HOW TO CHANGE ACCOUNT OWNERSHIP (clickable link)
(when you choose an account from the drop down menu it will tell you if the account is restricted or unrestricted. There are steps you have to do to make an account unresticted before making it the primary account. There is a note in the post I linked to about how to do this)