Hi there,
Just to chime in what everyone else is saying....
1. Once you accept the unconditional offer, your CAS is issued. I was going to hold on to my actual acceptance letter, as I wouldn't have gotten the CAS without having been accepted.
2. As long as your official transcript clearly states the degree you've earned, and the date that it has been conferred, then you should be fine. My university would always seal them in an envelope, and stamp it all over the place, saying something like "only official if sealed" So, before they seal it, make sure it has all the information exactly how you need it.
3. Yes, it should suffice. This is what I was told by the University of Nottingham:
Visa Application- in a previous email I referred to a process for adding the information about your loans to your CAS statement. This system has changed as a special agreement has been reached with the UKBA in the US. The UKBA will accept a specific visa letter from the University confirming the loans we have originated for you. We will produce these letters for you once the loan origination has been completed.
(it goes on with some school-specific details, but you get the point)

Good luck! I'm applying tonight (pending any disasters)--just finished gathering all my supporting evidence for Appendix 8.