If you want to add a runway, then you shouls get rid of the everything not on the main deck above the height of the first and last guns.
If you want more guns, that may not work because like the Agincourt, you would have too many big holes along the center of the ship.
Adding smaller guns is a given because you're lack even in the secondary battery. If I were you drawing a ship this large for the WWI-WWII era, I would end up drawing a ship with 15-18" guns, 4-even 8" secondaries, AA, then MGs-all on the same hull.
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Puerto Oeste - AU - WWI-WWII
Do you mean the platforms on top of turrets or something like the Furious when she was built? Or the Vindictive? Or the Akagi when she had multiple decks operating biplanes?
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Puerto Oeste - AU - WWI-WWII
Just look at the "average" kind of battleship of the same era. Casemates or early turrets would make up the secondary battery, usually of guns up to 6 inches.
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Puerto Oeste - AU - WWI-WWII