You want a super heavy gun platform?
Try a large structural framework, 5km high and wide, 500M thick.
Layer bonded superdense armor 5M thick on the front with 20M of rock in front of that in a cable web.
Mount a spinal mount sized weapon, PACC or Meson gun, at a random 100M to 250M intervals.
Mount turrets at 10M intervals across the face, a mix of all types.
Install missile bays anywhere you can fit them in.
Build a grid of power plants behind the big guns.
Hugh fuel tanks around the perimeter.
Bury your screen generators in the open framework betwen the spinal mounts.
The support facilities; State rooms, work shops, cargo holds, station keeping drives, computers, control rooms, R&R areas, and anything else to make life interesting built as the back wall of this monstrocity.
It may be wise to put a few turrets on the back and sides to keep the end runs from happening.
Paint a bullseye on the face center, surround with big yellow smiley faces.
Collect your paycheck from the happy admiral as he checks out his new toy and get out of town before someone tosses an asteroid through it...
It's a traveller style Maginot line.