Concerning CE Items and the Head Start EDITED FOR CLARIFICATION:

Any characters created during the head start will have access to the exclusive faces. However, they cannot change their face until the CE Product Key is entered.

The answer will be obvious once you see it in action, but for now let me try to explain. Players will be able to create and play their head start characters, however, during the headstart they will not have access to the in game bonuses provided with the collectors edition. Once a CE product code is associated with their account they will be able to use them post launch, this includes everything from the exclusive faces to the cloaks and everything included within the CE even on characters made during the head start.

What is this new "Mythic Account Center" and is it different from the Beta Center?

The Beta Center and Mythic Account Center are separate tools. In preparation for live we are phasing out the Beta Center. The new Mythic Account Center (current Dark Age subscribers are already familiar with it) will serve as your portal to all your Mythic subscriptions. If you have not done so already you do not need to apply a code to your Beta Center account, all invitations will be handled via the Account Center.

I hope this has helped to answer some of your questions, have a great night and stay tuned for more info. Exciting times ahead, we'll do our best to keep you in the know!