Ahhh, you want hard core technobabble. Ship sizes has been one of the on-going issues with Sins for the longest. As one of the fan-lore writers, we used ship complements to figure out ship sizes. Example...

Does it look like this TEC Colony frigate can hold 500 people. It looks like it can barely carry the 189 troops marching to it from the Rebellion trailer. Any "hard" facts came from the gaming community in order to add continuity in the fan fiction.
As far as weapon load outs for the various ships, again. From what is established in game, we have elaborated in fanfic as far as damage, weapon power. And of course, a lot of embellishment...