Here is a design sketch I've been working on since yesterday morning. It's the Strategic Space Command warship Ninegal - currently called a General Deployment Vehicle (GDV) but I'm considering alternative designations. The total length is around 2100m.
From front (left) to back, the sections are:
- Command
Habitat
Water
Power Plant 1
Exotic Geometry Motor
Power Plant 2
CHON storage
Cargo
Newtonian Motor
And those are radiators, not solar panels. The probably need to be re-sized depending on the actual peak output of the nuclear powerplants and the gross heat-bleed from the Exotic Geometry Motor. The Newtonian motor is probably a VASIMIR, since you would want to maximize the ΔV of your backup motor rather than its maximum thrust.
This sketch is missing a lot of vital parts, however. I have not allocated room for a primary laser, nor docking for scouts, shuttles, combat drones, or missile buses. A ship like this will need all of those things.
For comparison, see this Logistics Support and Command Vehicle:
I forget how big this is . 600m?