I like everything you said, except about the message poppups
Hoi already has a lot of popups, I wouldnt like anymore to be shown by default. Maybe be able to look at a screen when the battle is over that shows damage taken, and how a ship was sunk.
Aye, that's a fair point. I wasn't really wedded to pop-ups (although knowing one of your two BBs has sunk may be a good reason to tell the other one to run away, so I could see where it would be useful), more agreeing that it would be valuable for both gameplay and immersion to have some kind of commentary around the critical hit, be it in the battle results screen or somewhere else. Personally, though, I would like to be notified when Hood had exploded so that I could tell Prince of Wales to back off, if it wasn't going to do that anyway - would be a bit sad if UI limitations meant two BBs were lost instead of one.
I guess 3 in every 100 shells hits, and of that maybe 5 are heavy crits, 15 being normal crits?
I'm not expert on the stats, but my understanding based on foggy memory (take with grain of salt) is that at Jutland (about the best case study we have of lots of heavy shells being thrown at each other), for well armoured ships (ie, not discounting the British Battlecruisers getting a pasting, and just looking at the BB on BB action), is that 3-5% of shots fired hit. However, not a single British or German BB had a Hood-like explosion, despite numerous hits, which would suggest the 25% 'heavy crit' is on the higher side for shells in that situation.
It'd definitely be good to have different percentages for torpedoes and shells - if a torpedo hit, it was far more likely to cause serious to catastrophic damage.