I am working on a second one ( around a 1/3 of your size ) the hull is finished but it wants to fold in half when I throttle up. You will defiantly need struts.
I made a Infinity that carries frigates. Here is the link to it. http://kerbalspaceprogram.com/unsc-infinity/ Also, I've seen your infinity that you are working on, and I'm impressed with its size.