If you are upgrading the 'base' system, I'm told you do not need the speaker brackets.
Part of the upgrade to the premium package is that Ford puts a $3 dollar speaker in as opposed to the $2 dollar speaker in the base.
The infinity's do not come with an adapter, or screws or speaker wire for that matter. This was news to me as I had used infinity's in my Acura and all the hardware was included. I bought the Metra adapter.
Next weekend the rear's will be changed to 6832's (but I getting help with those). There is a video that shows someone replacing their rear deck speakers and reversing the plastic grommets for the screws. That way if you ever want to change them again, you can work bottom up as opposed to the top down.
Also I plan to install baffles on the rears (forcing the sound into the car), and tap the leads in case I want to install a small powered sub in the trunk (used for speaker level inputs on a Bazooka or Basslink).