For starters, anything above 16.1" (Nagato's gun) is not going to be considered.
That's the problem of going down the 450mm route you let everybody else do so and the treaty's collapse, so you will face 18' guns IMO and everybody who doesn't drop out of the race gets to spend more money (and a if you don't you are making the most expensive BC ever).
Armor is likely Italian Terni Cermented Armor, given that France and Italy are the main investors and supporters of China.
Good but will not be cheap (and was never built in the thickness you will need, the IJN stuff was deliberately cheapened and make to be made very thick)
I suppose the IZ should be around 20~30, so we're looking at 380 mm of belt armor after taking into consideration the angle.....Belt slope should be at 15 degrees.
In that case you will need a lot more weight in the belt, and it will have to be much deeper than 4.6m (16/18 shell will got deep and the angle cuts the real depth).
BTW, was British Cemented Armor that better than US Class A Armor? I noticed how relatively thinner armor could be used for protection.
I think the story was that the US did lots of tests with smaller scale as its much cheaper and remember 20s/30s budgets and the fact that you need to do lots to get statistically significant results (3' shells I think) without realizing that they should have validated it with a few 14/16' tests to test scaling laws). (If I remember correctly, The result was that it was to hard (the face hardening was done to deep ?) to work optimality and by the time they realised (when they had budgets post 37-41) its was to change as it would add big delays to the needed production)
JSB