keep in mind that the battleships build around 1920-30's were about the maximum size ships could be build at the time. that was in part due to the docks and harbours of the time, but structural concerns are an issue as well. material strengths and construction methods have come a long way since then, and civilian ships have grown a lot, but even keeping that in mind there are reasons why aircraft carriers have stuck to their current size, not that much bigger then yamato was.
When I decided to convert this project from a real world scenario to my AU scenario, I gained he ability to be more loose with how technology flowed. In my AU, Seaplanes are more dominant, there is no event similar to the Russo-Japanese war, architecture is more 'extreme' and some technologies are more mature or less mature compared to our world (with a good 20 year period of wiggle room compared to our world).
For example, here is a giant bridge I have been working on. Or a cross section anyway.
For a 20's-30's era ship. (IMO)
As for bigger guns, I am likely going to go bigger with the ship hull to accommodate the 22" guns. As for the 10" guns, good point. Based on looking at some gun fire rates, even dropping from 10" to 9" quadruples fire rate. So what I think I will do is add triple 6" turrets. Not automatics, as this ship is more of a 20's-30's era ship.
I would have 8-12 big guns 22' or something (not sure bigger is actually worth anything really what are you shooting at ?)
Then add 8' guns to kill CAs/Cls (you could go for 6' but see below and 8' are probably better to kill CAs/CLs especially as you will have lots of them anyway)
I will also up the 5" guns to 6" guns in single gun turrets. The single gun turrets will be dual purpose, the triple gun turrets will not. I will then likely have a re-armed variant with its triple gun replaced with double 6" automatics and 6" automatics for its single turrets. All dual purpose as part of an anti-air re-armament.
Personally NO you cant get a DP 6' in 20-30s (without bending the rules shells are just to heavy to move by hand and 'robotics' to immature) the first DP 6' are 1945+ and they are huge you cant refit them into old singles (or even really new twins into old triples) I would keep 5'/38 or 4.5' or just go with AA guns 3'/4'/105mm as you have 8' guns to kill any surface threat ?
As for assumed AA armament, I am thinking a mix of .50 cal, 30mm (similar to the MK 103 germany used) and 57mm guns.
Very wide mix !
.5 is ok for time period but near useless (at least later on), 30mm MK 103 is a 1940s gun and the 57mm are 1950s+ guns (but very good) and why would you bother with the .5 if you have 30mm/57mm apart from 2 to shoot at smugglers (and this is not a patrol ship !) its just a waste of crew.
I will likely skip on the 3" guns if I am going to have a ton of 5" DP guns and later 6" DP guns.
Sorry if I don't understand but doesn't this conflict with the high up ? IE 6' then 6' ?
I just like the fire rate of the 6" guns. I feel like I might go for larger numbers of 6" guns (triple instead of double turrets) and use that quantity to make up for the lack of 8" guns.
The DP 6" guns come later after a refit/re-armament. the 5" DP guns get replaced with 6" after the re-armament 15-20 years down the line. Sorry if I wasn't clear on that.
As for AA armament, I will definitely keep the .50cals but over the ships lifetime those will likely get gradually replaced save for a handful on the main command tower. As for the 30mm guns, instead of being based on the MK103, lets base them on the MK101. The 57mm's are a challenge. I want something that is rapid fire and above 45mm.