Okay for any who would like to read my story for greater details on what's up with the design philosphy (and just for kicks) read go
Here
As to what the GFG is, and what it does, the Gravity Focusing Generator produces a gravity field around the ship which enables it to travel through a warp point, if the GFG were not there then the crew would be turned into a substance with the consistancy of chunky salsa unless they got extremely lucky.
The part you see on the superstructure is only one of three (3) parts of the system, there is a focusing generator for and aft of the main super structure element, an invisible energy "stream" connects the three generators to establish the gravity bubble around the ship, however because of the fact the larger the ship the larger the central GFG required, by time you get up to anything bigger then a cruiser the GFG can no longer be mounted in a small unit atop the superstructure and instead requires a much larger support structure.
As to why Icarans fight broadside, shields in the Icaran universe do not work like those of "star trek" or other science fiction, in that the energy barrier that makes up the shield works both ways, basically you can't shoot out through your own shields as you'd just be causing damage to your own shield when the energy weapon and shield barrier interacted.
Thus when a starship fires it's weapons the shields to that whole section must be dropped, the Icaran naval doctrine decided to maximizing firepower and armor to the unshielded section they would have a broadside arrangement for their main firepower, having "chase mounts" with significant firepower foward and aft so that they can sustain fire upon the enemy even while they are approaching for a broadside engagement.
Being that no starship can truely fortify it's for or aft sections with any great deal of success firing chase mounts is done with great care.