Personally I would start by thinking through the history of your ship ?
When was it built, when is it depicted and has it been rebuilt in the image shown ?
This then could give you the date systems where added to the ship (and any taken off), I'm saying this as this hull looks early (as do 6") and the much later missiles radars, so it looks like a rebuild to me ? If it is then maybe think what would come off to fit the missiles etc ?
Yes, that's an important question. At first I was drawing this ship as part of my alternate world (in my childhood I have "invented" my own paralel world like Westeros or another, but with the technology of the mid-20th century), but then I realised that I am not skilled enough to design ships "from zero", so now I am thinking that the cruiser will be part of the future Polish AU, which will be lighter than making the whole imaginary planet
As for the purpose of the ship - well, I thought that it's purpose is to provide anti-aircraft, anti-missile and anti-submarine protection for the fast carrier groups, to provide NGS for the coastal landing operations and to fight with enemy ships, of course
The year is approximately 1973, but I have chosen the GW25 hull because it's large enough to place weapons, magasines and stores for such number of tasks. 6 inch guns were chosen because I think they are much better for the NGS and the CQ than the 4.5in guns.