I haven’t found grapeshot to be very useful. I like double shot in situations where I might otherwise use grapeshot, and raking the stern is the best
I generally target the foremast manually. I don’t use chain shot much, preferring to target mast, but I could see using chain if your guns are too small for mast. In Total War: Empire, I focused on chain because it had a longer range than round (in addition to damaging sails to allow you to control engagement.) In UA:AoS, chain has a shorter ranger than round shot, which could be more realistic, but makes it less useful.
The idea of targeting the waterline is interesting.
I have used the Congreves and the EIC line a lot, with occasional Woolwich guns for range. I think a lot of the battle is 500 yards or closer, so I have wanted guns that had high damage and decent penetration out to 500 yards. Most of cannonades seemed to have too little penetration (except for ultra short range).
it has been interesting that a cannon’s utility doesn’t seem that tied to price. Certainly, the bigger guns are more expensive, but within each size the price doesn’t seem determinative. Eg, the J&H guns are expensive, but have little penetration.
In addition to providing more damage for their size, I like how the Congreves and the EIC cannons reload quicker - due to shorter barrels. Quicker reloading is valuable for getting more focused lead on target.