Half range sounds fine, but what about the shorter ranged guns?
It depends on what the smallest guns represented are. I notice that Graf Spee's 5.9"s are simply rolled into her 'secondary armament', and her 10.5 cm AA guns along with the British twin 4" mounts are classed as AAA.
It looks as if lesser weapons are just going to be abstracted out, rather than dealt with individually in detail. Well, that's OK.
You could put a cutoff for ranging in at 6". Due to their unstable nature as gunnery platforms, destroyer shooting against ships wasn't much use outside 2-3000 yards (US destroyers did fire at greater ranges in the Pacific, but I think that was more for moral effect). Destroyer gunfire could be limited to 6" maximum, and only effective against other DDs or smaller.
I've been racking my brains to come up with any example of a battleship using her secondary guns against warships, and I can only think of one - the Bismarck during her last stand, and notably ineffective they were too. I'm not sure if Spee used hers at the River Plate. I stand to be corrected if anyone knows differently.
I'm not at all convinced about the 'crossing the T' gunnery modifier. The point of crossing the enemies' T was to bring your full broadside to bear, while he has his aft (or forward) guns masked. At long (plunging fire) range, the ship's target area is basically the size of her deck, regardless of facing. Except in rare point-blank engagements (Cape Matapan, Narvik), WW2 naval gunnery was an exercise in area fire, which is why the number of guns firing is so important, and the precise orientation of the target isn't.
An example is the loss of HMS Hood. Hood blew up at about 12,000 yds (edit after fact check - about 16,500 yds) from Bismarck - inside her 'zone of immunity' where Bismarck's 15" shells would have been arriving at a shallow angle and hitting - and likely being stopped by - Hood's 12" belt armour. Admiral Holland knew this, and having approached the German ships head-on to cross the dangerous plunging fire zone as quickly as possible, he was in the act of turning to present Hood's broadside when she exploded. Just why Hood died when she did remains a mystery.
Identification - Langsdorff mis-id'd the British ships at River Plate, Hood and Prince Of Wales initially opened fire on Prinz Eugen, mistaking her for Bismarck, and later in the hunt for Bismarck a strike of Swordfish from Ark Royal made a very enthusiastic attack on HMS Sheffield (fortunately with dud torpedo fuses). There should be something in the rules for ship recognition.