You might want to go with a sphere inside of a gyroscope.
The sphere would be the living and work space, while the cage around it would house the armaments and the engines.
I'm thinking something like this "untippable" gyro-bowl. (Link for image and description only. I'm not suggesting a product or promoting a retailer.)
This allows you to swing your engines and weapons around without having to go through the problems, and inertia, of changing the orientation of the whole ship. I'm sure I've seen this somewhere before, but I can't remember where. I want to say there were moveable weapon systems on the skin of the Star Trek: Deep Space 9 space station, but that's a vague memory of a semi-generic space battle.
Anyway, this would allow for quicker changes in angles of attack and defense, sort of like the Marksman-H training remote from Star Wars.
The problem with that is if you have a single cage ring, your engines are on the same platform as your weapons, so you are limited in your movements when firing the weapons during battle. With multiple rings, you are limited by not wanting to fire a weapon into the outer ring(s), even though it would allow for more total weapons platforms without hindering interior living space as well as giving the ship more maneuverability.
With enough rings, you could have a fairly flat looking ship with just a "bubble" in the center, but then spreading the rings out, you could become an armadillo version of a porcupine with weapons pointing at nearly any 3D point in space.
Gyroscopes are nothing new in spaceship design and could work in multiple capacities, besides as a weapons and engine platform.
And really, it doesn't have to be exactly a gyroscope. You could have a single axis of rotation along the direction of travel, and then a series of rings attached to it to have a similar effect. The engines could then be fixed to the main body and the weapons rotating around that single axis. Again, this could be flattened for normal operations and deployed for battles or used as armor for an unusually dense area of space debris. At this point, your center wouldn't have to be a sphere, but a sphere has the largest interior volume for it's surface area. The problem is that you've put all of the moving parts in one location for a single point of failure. This may mean that maintenance is easier, but crippling your ship becomes easier, too.
The sphere has the smallest surface area of all surfaces that enclose a given volume, and it encloses the largest volume among all closed surfaces with a given surface area. The sphere therefore appears in nature: for example, bubbles and small water drops are roughly spherical because the surface tension locally minimizes surface area.
One problem with a fixed engine location is that you might want to hide your engines, so the enemy can't fire on them directly. How many times have we seen a space battle end with someone swinging around behind the enemy to fire on their engines and disable them? Well, not anymore. The enemy goes one way around you, and the engines go the opposite way around the ship.
- But wouldn't that put the living space in danger? Maybe, but why not have the weapons or heavy armor swing around to face the attacker at the same time?
- Oh, the aft shield is failing, because they are concentrating their fire on it? Swing another shield around to help or replace the failing or overwhelmed one.
- There's multiple bogies? That's why we have multiple rings that have more than just one weapons system and shielding on it.
Yes, this has a lot of moving parts, but it significantly increases the surface area considerably.
Also, once deployed, nothing says the rings have to keep moving with respect to each other. Keeping them locked together will help prevent self damage, but can still allow moving them around the "bubble".
And the rings don't have to be flat faced. They can have a curved or beveled face, so they can fire at more of an angle than radially from the axis of spin. This would produce more of a cross-fire pattern, allowing an angle of attack from more than just a single ring at a time. This makes not hitting yourself more difficult, but that's what automatic safety systems built into the ship are for.
Sure, rockets and torpedoes can change direction, but that uses a lot of propellant and time. The shallower the turn, the faster it can home in on the enemy.