No, Battleships are reported to be a about a dozen or more Kilometres in length, it's just that their Shield Bubbles extend out to that far, rather than hug the hulls of the ships like Star Wars.
Are you sure? That sounds VERY odd, so I would like to ask for a source on this.
Frankly I don't see the problem with using BFG stats for BFG fleets since they are the ONLY NUMBERS TO GO ON. Finally with the Fire Warrior scene we actually have CONTEXT for what those numbers actually mean. If the ONLY number you had for Blasters were from an RPG book then yes I would allow them and argue against them as if they were your word of god, but they aren't, you have films and novels and comics and cartoons and such to back you up. It's just like your Star Wars Canon ladder, my numbers are still good as they have not been disproven by a higher source.
As for all the technical stuff about shields, Based off of the amount of power shown and put into context against the ships stats. I would have to say that each point of Shield in BFG would be able to take around 750 Teratons per second second.
Because the game mechanics are just that, game mechanics. In the novels you have very different things going on, with space marines dying in one hit, being ripped apart, IG soldiers taking on bigger enemies than they ever could in the games, etc etc.
Using your game mechanics to calc idea, then the Venator at full firepower can take out a shield and have 50-110 teratons left over to hit the ship.
Yet Azure Hammer Command seemed to only be as strong as One Sector Group... and they also only oversaw One Sector...
"A standard Sector Group was composed of 24 Imperial-class star destroyers."
Azure Hammer Command
"At its height, this mighty fleet consisted of the Super Star Destroyer Whelm and 57 other capital ships."
You should have also clicked the Sector Zero link instead of simply skimming it's name.
"Imperial Center Oversector, also known as Oversector Zero, was an Imperial Oversector."
Ok, who allowed the Slaves to form a Union? I bet Somebody got Choked to death over that mistake.
The Death Stars required private shipping companies to bring in the materials, those are who I assume the "labor union disputes" refer to.
In fact, when word of the Safety of the new conflict zone (as well as the chance to fight along side their God) arrives back in the old galaxy, I would expect many hundreds of sextillions of Guardsmen to be signing up to be shipped through to the front.
And how long would this news take to travel? It would still take months to reach the entirity of the IoM, and then months for them to even reach the SW galaxy and get anywhere important there.