"The Alaska/Enterprise-C was to be the pioneer of a new sub-type of the Ambassador-class." I'll assume that the old sub-type would be Mr. Probert's original design?
A nice history overall. I think the Ambassador / Galaxy history might be a little off-topic (although interesting).
I might also suggest throwing in a ship or two a) not named Enterprise b) not captained by Star Trek stars. Especially when you stress over and over how many of these ships there are and that they are the backbone of the fleet for decades to come.
It takes a lot to get me to read that much fan text. Even more to convince me that this might be "the way it happened." Very nicely done.
I second that, maybe a couple capsules on some of the more famous examples... We've seen at least two on TNG captained by "somewhat" famous captains... Figure those two and two more totally made up ones.
Give the green-light and I'll start the Conbabulator churning.