I am no expert but have been testing as Japan the shipbuilder somewhat. Its still very vanilla but it works as designed. Unfortunately the design is very simple. If you increase ex. armour you get more armour and lower speed. You should also get lower range and higher fuel, HP and visibility but you don't. Fun but not great. It's the same with all your choices.

Some stuff is absurdly cheap like armour and motors. Ex. a (I) 40 mm Belt/ 20 mm Deck cost like 380 IC while a (III) for 100 mm /60 mm cost like 700 IC. The improvement is BTW not really reflected in the stats.

Some stuff is absurdly expensive like AA level I as you pay like 13% of the ship value just to change it and then for the equipment.

It was really not necessary to create a Heavy Cruiser Hull and then change the original Cruiser Hull into a light Cruiser Hull. The game mechanic considers a Cruiser with Heavy Gun (200 mm and above) as a Heavy Cruiser. If below it's a Light Cruiser and treated as a screen. Try changing Tone to 155 mm (in vanilla) and it becomes a light cruiser. Its the Gun not the Hull.

IRL you could basically build an unarmoured Heavy Cruiser and an heavily armoured Light Cruiser lets say for AA or stronger screens? In game play it is quite important as you need a lot of screens to protect your caps so I believe CL's are nice to not dilute your cap defence.

In Japan you now have a 1934 Light Cruiser Hull and no 1936. Only a 1936 Heavy Cruiser Hull. Maybe not a big issue but I wanted to create an AV Cruiser as light and FAST as possible with 3 x Aircraft and use it as a ISR screen (as they did). I will the have to use the 1934 which is ok as there is no way to turn the CA into an LC.

BTW the Akagi and Kaga are Converted BB Hulls and therefor have no armour as the need hangar for 60 planes. Not so historical but not much to do.

I really recommend the Naval Rework II to be included! It might save you a lot of time for other important stuff. At least you can get a lot of inspiration there.

Great mod. Wish I could help.