-> Size
I don't know the exact lenght, but I think it should be something between the Orion and the other destroyer from FS2 (forgot the name, Hekate?)
->Human, Vasudan, Shivan???
Basicly its a Human Vasuda design, but it has also a Shivan influens. The Shivan part is there, because of a quite easy rule in Warfare...learn from your enemy!
( Friends teach you what you want to know, enemys teach you what you need to know)
But it follows also a new way in fleet designs. With the advantage of Bombers and Torpedos, small vessels (Fighter/Bomber) become a real threat to cap ships. Beside that fighters and bombers can be produced faster and easier than Capships.
-> Differences in the Design
There are two designs in the new Carrier class. Human use more bigger guns(beams) on the Templar combined with a heavyer armor. Drawback is that the Human Templar is slower than the Vasudan one. Also it leaks the point defenc capabilitys of the Vasudan design.
The Vasudans use manly antifighter beams, flak and only 2 heavy longrange beams. The armor is weaker than the Human design. Advantage is that its faster and it carries more fighters.