The disc drive on my PC a bit dodgy at best, I'm about to pre-order the MoP CE and just would like to clarify that I can upgrade my account via battle.net then download the client, thus not having to use the discs within the box?
Buy the Collector's Edition -> Use the CD-key within to upgrade your account in Battle.net Account Management -> Load the client -> Automatic download! No disc required.
Client is the same for everyone. Only difference is what content you have access to, and that is determined by the expansions activated on your account :)
Correct. My workflow was assuming that the OP was going to be activating their CE on day one.