Deckplan Syndrome #3: "tacking on extra weapons anywhere that looks cool"
The biggest misunderstanding of all has to be the subject of weapons. Fans (and WEG) tend to just bolt-on as many weapons as they can - declare the ship to be "kool" and "awesome" and walk away satisfied.
"Hey dewd, I just designed the kewlest most awesome fighter in the galaxy! ... the [randomn letter]-wing, with way more weapons than ANYTHING else!"
*sheesh* ... if it was that easy, don't you think we'd see things like that flying around now?
NO - weapons systems are BIG. Think ice-berg. The gun turret is just the tip. Behind the scenes are layers and layers of infrastructure.
- Weapons needs MASSIVE power feeds (and "ammo" - whatever that consists of in the StarWars galaxy)
- they need solid and rigid bracing as their recoil and just the stress of their rapid movements place immense strain on the hull
- they need targetting systems, control systems, cooling systems
Consider this: a WW2 battleship displaced about 20,000 tonnes. It was the size of a football stadium and needed 1000 crew ... all just to get about 9~12 largish cannons from place to place. Every other system on the ship is subordinate to that. A battleship is a gun-platform first and foremost. If it was possible to move that kind of firepower around more cheaply and easily, don't you think they'd have done it? A battleship turret is a massive structure SIX STOREYS HIGH. We are *not* just talking about whipping out the model glue and sticking some more guns on every flat spot of hull!
Earlier i suggested starting with drive systems when you design. In a battleship however, they started with the guns, their structure, power systems, command and comms, ammunition etc. Then the figured how much mass that was, what sort of hull was needed to carry it - then power systems, armour etc etc etc A battleship is a balancing act between firepower, armour and speed (just like a battlefield tank!) and you cannot max-out any one of those without costing elsewhere.