First will be - main caliber, obviously involving a ship's main guns, turret and ammo.
Next comes the low caliber - which includes all the small calibers for ships that have many.
3rd will be torpedoes and launchers if any are available. Obviously that involves better launchers and torpedoes. Being an avid Silent Hunter 3 player I can immediately point out the importance of good torpedoes and also - what type of torpedo you fire - newer is not always better. German gas torpedoes have a visible bubble trail, but could move faster and with longer range than electric ones.
AA guns are also united in a single ship module.
Onboard aviation is also a single ingame module. For carriers obviously that involves the carrier air group, for battleships and cruisers - hydroplanes. Carriers might have an extra little bit - not sure if bomber wings customization will be available - the difference of taking off with bombs or torpedoes could change the battle.
Detection and fight control system is also another module - I'd guess that involves view range and weapon coordination so it might affect accuracy too.
Finally - ship hull. I believe that one is self explanatory - better hull with more armor, HP and so on.
What I am curious about is customization. In World of tanks - most of the time the top modules are the best, in some rare cases you can pick a different main gun.
However in WoWs there are many weapon systems and the decision which is best might not come so easily.
Pick weapons for example - you got main guns, secondary guns, AA, torpedoes and planes.
When it was released, the IJN Yamato had an extra set of secondary guns.
However by 1945, those had been replaced by more AA guns because of the ever greater threat by US carrier aviation.
How does that translate in World of Warships terms? Well - in a battle where there are few or none enemy carriers but plenty of lighter ships, your Yamato would benefit more from the extra secondary caliber guns.
On the other hand - in a battle where enemy aviation is strong, more anti-air capability can save your skin. Of course it all depends on Wargaming...they might take the easy way out and do linear upgrade paths.
