The difference between shields, ships, and weapons is that you can only mount equipment that your ship can handle. Let's say you have a butt-kicking Starflier, you can only mount I think level 2 or 3 guns since your ship doesn't have the power capacity to accomidate higher-power level guns and equipment. But let's say you have a Sabre or Titan, I mean, those ships have totally tricked out power ratings so you can mount level 10 guns and equipment. Because the ship can handle the guns. Your level (displayed on the Reputation icon) also determines the weaponry you can buy. You have to be able to handle the weapon's power.

As for your first question, each ship you buy has a pre-set weapon arrangement. It might come with 2 guns (of the ship's home world, of course) already mounted. Let's take the Starflier, on the first mission, it comes with 2 Justice MkI's I think. Since the Starflier is a Liberty ship, it has Justices because those guns are Liberty ones. And what about a Valkrye? A Valkrye would have 2 guns which would be Stealthblades, the Rhineland cannons. As for the shields, I can't help you, but I'll tell you this, some shields can only be mounted on Heavy Fighters, others on Light Fighters, and still others on Freighters, there are also level restrictions. You have to choose the shild class that is the class of your ship and then look at the levels.

You probably know most of this, so don't eat me if I didn't help any. I hope I was of some help though.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

During my travels, I have learned that being optimistic doesn't always help, hey, the light at the end of that tunnel may be an oncoming train.