I think you also have to think about how you will be cut down by LNT, You will be cut down to 9 ships (unless you are read are with my new BC completion suggestion? I think you need more than 2 15" ships if you are to be considered a power with IJN like numbers) at that point do you cheat or keep one of the old BC as a training ship or cut both to save cash?
It would help if we could have more info about the nation to talk though ideas? Do you have any CVs existing on 1921?
I think most likely fleet is,
2BC 380 completed after treaty (a deal for lacking 16" ships and to swap with the 2/4 BC/BBs), 2BB 380, 4 BB 320mm and 2 BC 320mm.
With 1 CV 32,000t conversion to use spare hull and maybe 1 earlier experimental light CVE ?
This gives you 49,000t to build more CVs (27,000t limit in WNT, later 23,000t 2LNT) so you can build 2x 24,500t ships in 20s/30s.
You would also get 100,000t each of CA, Cls and DDs to build and 50,000t of Subs.
More info on the fleet and the country.
It is a kingdom located half way between New Zealand and Chile.
The mainland is located on a peninsula of the Antarctic continent. It also holds large number of islands on South East Pacific.
Id did not draw a map because I am really bad at maps.
As for the fleet, in 1908 when they started building Dreadnoughts captal ships.
The fleet consisted of 8 pre-dreadnough battleships and 8 armoured cruisers. Plus 21 light and armoured deck cruisers. No destroyers but large number of Torpedo boats.
By the time of WNT only 4 pre-dreadnought 2 armoured cruisers remained in service.
Production of cruiser continued but not a single unit was larger that 6000t.
Destroyers were not build as it was belived that they are far to remote for their ships to meet a enemy Torpedo boat in combat.
In 1913 2 sea plane tenders were laiddown, in 1917 an experimental Carrier was build. 12000t, 26 kt.
When the WNT was signed there were 3 battlecruiser in construction. Those ship were laid down in late 1918.
Those 3 32000t ships were armed with 9 320mm in triples design speed was 31kt.
In carrier conversion those ships will get tinner belts, without the main battery, I think they could be slimmed down to 27000t. If Japan sold Akagi and Kaga being 27000t standard I think I can too.
As for cruisers, I was thinking 8 or 9 175-191mm range guns. Light cruiser would be 6-8 150mm guns.
As for the need for more that two 380mm BB.
That as many as they have.
2 380mm BB, 4 320mm BB, plus 2 320mm BC and 2 280mm BC. This country does not have the ambition to be equal to IJN.
They are quite happy with being around Italian and French fleet in size. That is as much as they can afford.
They pushed for the all 3 BC to be converted to CV because they feared gap in capability.
US and Japan got too have 2 large and one small carrier each.
Royal Navy has 3 large and 3 smaller plus a number of decked over large cruisers.
They have faith in torpedo. They see the carrier as a way to deliver planes armed with torpedoes to any evetual fleet action.
As for why keep the old BC armed with only 280mm guns?
At this time only two fleets in the world have BC, Japan has 4 UK has 7 that will soon turn to 5.
8 280mm is still enough too make The Princes Royal or the Tiger think twice about engaging so far from friendly ports.
Thos two old ships will be kept in service till year 1930. After that New design may be contemplated.
The plan is now to have the battleship holiday and then in 1930 laid down six hulls 3 fast bb and 3 CV.
At present they have no idea that the LNT will extend the battleship holiday for 5 more years.