If I switch to ICloud mail how do I notify everyone of the change?

You would have to email everyone you know using the new account so that they can add the email address to their contacts.

To create a new icloud account, go to

http://www.apple.com/icloud/setup/

I've switched email accounts before, and I found that emailing everyone just annoys them. Rather than do that, set up your Gmail to forward to your iCloud account. That way you still get the messages, and can notify everyone more subtly by adding a signature in your iCloud account. They'll all eventually get the picture.