The Hanoverian Confederation builds these huge vessels using orbital resources. They are strongly armored with multiple layers of ablative and reactive armor as well as traditional hardened plate armor, and carry a large supply of missiles. They have multiple fabbers, one at each end of the ship and in the middle, to make parts for when underway, as well as raw materials depots in various spots. They typically are combined with refinery ships that are capable of taking in raw asteroid and cometary materials and turning them into the refined materials needed for the fabbers. They also have large nuclear reactors by the fabbers, as well as laser turrets on all four sides of the ship near the reactors.
The Hanoverian Confederation is unique in the known galaxy in that their ships are fully staffed with humans rather than with robots. If a hull plate needs replacing, they put a human in a space suit that’s almost a robot and send him out on the hull. The Confederation developed nanite technology to repair the radiation damage from doing this. Other cultures in the surrounding area find the Hanoverian practice to be bizarre. Their ship AIs combined with robots do most of the heavy lifting, with a small command staff to set policy.
There is a reason for the Hanoverian practice, however: The nanite technology developed to fix radiation damage also extends lifespan basically forever — people develop to their mid 20’s, and basically stop aging. Thus the only deaths are those due to gunfire or accident, and they have a large number of people who they need to keep occupied or they’ll get up to trouble. It’s a jobs program, in other words — one that results in Hanoverian battleplates being tremendously large for the amount of firepower they pack, large because they must haul all this meat and the supplies needed to keep this meat alive that competing confederations don’t need to carry. Most other star nations have warships packing similar firepower that are perhaps 20% the size of a Hanoverian battleplate, meaning that if they were attempting to overrun the Hanoverian confederation, they could make 5 times as many warships with the same resources. But the Hanoverian Confederation is *huge*, blatantly expansionist, terraforming every rock that’s suitable for terraforming (and some that maybe aren’t). They also have a very effective intelligence operations group that looks for systems that are becoming heavily automated, putting people out of work, but have not replaced the lost jobs with something else for people to do. These nations are offered a solution — membership in the Hanoverian Confederation, with its strict limits on what robots are allowed to do and plentiful jobs and places to emigrate to for the human population. Plus immortality — Hanoverian nanite technology is the best in the known galaxy as far as life extension goes. Many systems take them up on that offer.