Those assumptions about the visible form of the lighter weapons are correct. On a cgi-irrelevant but technically interesting note, I'm thinking the LTL are mainly very light-weight, rapid firing anti-fighter area defense, so the throw weight will be relatively low per shot but massive by volume. Well under 100megaton/shot is likely; enough to crisp a fighter but rapid firing enough to do point defense. Given that, the mediums take over the role of anti-corvette fire that LTLs might do on a destroyer.
The indented hangar areas are a bit less than half as long as an entire Imperator-class destroyer. I'm thinking there will be a series of hangars arranged like those in the Death Star equatorial trench - launch bays for shuttles and small transports, and space for TIE squadron racks. The hangars I see as largely external to the main structural skin of the hull, more built on top of a layer of armor with small feeds to internal magazines and power leads than really integral. That makes them a far less vulnerable opening into the ventral defenses, yet allows the ship to carry its own fighter escort and scouts.
By volume, if the internal space allocations are identical to those of an ISD then this ship should carry about 24 wings, and 24 legions (i.e. 6xcorps, so ~an Army sized formation). Since I intend for this ship to stand in the line (well, radically maneuvering swarm perhaps), the allocations will be much less. I'm thinking along the lines of 4-6 wings for the fighter group, plus transports and shuttles (heck, you could fit a couple of IPV/custom corvette patrol ships on racks in there for organic escort for itself or its attached bombers).
Troop wise, given the relatively limited space for heavy dropship assets, probably not much in the way of armor. Drop the surface base and engineering assets, won't need those in a squadron ship. 3/4 legions - enough for shipboard security and boarding action, and a useful enough capacity for dropping reinforcements into a recently bombarded world after the assault echelon comes out of accompanying ships.
Now for a long rambling post:
I imagine this ship is likely at the size limit for routine deployment. This ship gets sent out when real firepower would be useful, but speed and alacrity are still necessary, and an Executor would be overkill. In a sense, it is the evolutionary equivalent in the star cruiser weight range of the Imperator for the line destroyer and Executor for star battlecruiser/fast dreadnought. That is, at the upper end of the economical range for the category. Not big enough to blur the range like an Allegiance would for the destroyer classification, but spacious and balanced for the job in hand.
Which raises an interesting question: what is the real role of the star cruiser? For a destroyer, even as large as, say, an Allegiance, maneuver and acceleration are going to have to be dominant in their approach to battle; do not get hit by a real capital ship, like a dreadnought, or you are screwed. The successful designs, like the ISD, have the combination of power and stress tolerance this requires. Once you hit the level of a say, a Mandator, or an Executor, you have the strength to sit there, be a stable gun platform, and pound hell out of anything that blunders near you while gently wallowing in time with a line of sister ships.
In the middle are the cruisers, the "Anonymous star cruiser #1-5" range of ship. Probably too heavy to really dance like a 3500g-accelerating Imperator, but too light to stand there and suck it up as long as a Mandator. So what are they for? In a fleet engagement, I imagine they (or at least the bigger ones like this) would operate in squadrons, likely able threaten star battleships with coordinated fire. The biggest, like this one, may well be tough enough to take battery fire from a dreadnought, but unable to sit still very long lest the capital ship land a full broadside, and so must have the acceleration to do some footwork.
Separate from a battlefleet, it might lead a destroyer squadron, or operate as a heavy hunter. Likely this kind of ship would figure prominently in a regional or central reserve situation. Fast enough to run a wide variety of things down, and powerful enough to cull rogue imperial sector forces. Perhaps in the 3000-3200g range? Built strongly enough for tight turns, and with the power to make them.
Of course, the armament necessary to do all this, the strength and durability required, place a lot of demands on the powerplant to make it move at a survivable speed. How to reconcile all this? Strip out all the equipment that enables the Imperator to multi-role, and fill them with power generators and structural stiffening. Which, coming full circle with this remarkably long post, is why a ship with 25x the volume of an Imperator carries only 4x the attached fighter and troop assets.