The Gettysburg comes from Freedom Flight, SM2 (TCS Austin) and Super Wing Commander. There is nothing in the way of information beyond little things like that the Austin is bigger than the Claw. In SM2 the Exeter model is used to represent the TCS Austin/Gettysburg-class. Everything else is what Saga has brewed up.
In the first years of the war, I think the role of fighters was slightly smaller because there wasn't that many fighter-carrying capships around (from what we see in AS, although we see tons of fighters). You would see more small fleet actions between DD and CA-size ships. However, I think the "fightering up" of the fleet was something that happened quickly. We know fighter actions were common during the 2640s (we have things like Tolwyn's action at McAuliffe, Svetlana's father contributing to the loss of his carrier, Custer's Carnival, etc).
While carriers might have been rare (or at least small in number compared to the thousands of DDs and hundreds of CAs roaming the Milky Way), they were still the best means of projecting force in an area.
I imagine most of the war being fought in a similar manner to the War in the Pacific. Most of the engagements are between small naval forces, usually DDs and the occasional heavier ship. Think how many small fleet actions we read/see in the WC lore. The Movie related stuff is filled with ship-to-ship actions of DD and CA size ships. I see this as being the main way the war was fought. Corvettes, Destroyers, Cruisers in task groups engaging enemy task groups for control of areas.
Then you the carriers are jumping around from hot spot to hot spot, supporting assaults, raiding bases, defending others. Although, I see a difference when it comes to the heavier capships, because many of them will eventually mount decent fighter wings. So they become their own fighter support as well as mounting heavy anti-ship weaponry.
When it comes to number of carriers in service, I think that really depends on what date you are looking at. In the last 3 years of the war Confed suffers heavy carrier losses (I want to say 8 alone in 2666 according to ER). So that means in the early 2660s Confed had somewhere near 20 carriers. Now the galaxy is bigger than the Pacific, but given the make up of the US Navy during WWII the numbers make sense to me. Granted, I'd expect ConFleet to have something more along the lines of 30-40 carriers, but we know Confed starts the war at a disadvantage by not having the military infrastructure there to rapidly build large capships.
I have a bit more to say but I'm late for work now...so I'll finish up later on. This is a really interesting topic.
EDIT - still can't figure out how to post pictures!
There is a button on the toolbar for linking to a picture....I'm not sure either how to upload a shot directly into a post though...help anyone?