Why is it necessary to process the information after and have the credit card details emailed to you?
That is the difficult part. Sending credit card information in email is never recommended. You say you would delete it immediately, but when it comes as email it already passed through dozens of computers on the way to yours thay may not be so kind.
Ecart can do everything except safely encrypt and unencrypt your data. If I were you I would:
1) Forget authorize.net unless you can process the CC real time
2) Figure out a secure way to encrypt and unencrypt the ccnumber for storage
3) Store the encrypted CC information in your database and don't send it in an email
4) Send an email that lists the cart contents and links back to an admin section of your site, have that section login protected with securityAssist.
5) on the back end enencrypt and display the CC number to the logged in user.
6) manually process the card from that page and delete the encrypted card information so that even that isn't stored long term.
PHP has several libraries that will help with encryption. Support is correct they don't come with eCart and are not directly supported. However it sounds like you need to go down a route that isn't directly supported and I wouldn't suggest CIM in your case.