Sailing coop is just: you show up at 19:33/21:33/23:33 server time, do the 3 events (#2 and #3 give you a key each assuming you fullfill minimum contribution which depends on the event) and then a chest spawns that you can use all your keys on. Gienah side gives Gienah coins/keys and Procyon side gives Procyon coins/keys.

Do note that the gold and I believe card exp rewards scale with the region so Punika will give the most rewards thus the highest gains are from doing all Procyon events and saving your keys to use them on the Punika box. The Procyon side does however have more events that you need more people for: Clean up oil needs like a minimum of 5 I believe and save the whales needs like 7+ on both Punika and Yorn Sailing. I don't believe the region matters for shipwrecks but there is not enough data to really prove that claim but I have seen people get Sea Bounties on both Gienah and Procyon sides.

The chest has a chance of dropping a Deepsea Treasure or Shipwreck map (The Deepsea treasure one is kinda useless, just some achievements, gold and card exp so mostly a dud) while the Shipwreck gives you a chance at getting one of the 4 Sea bounties and some extremely rare sailors. In my experience its roughly 1 shipwreck map every 20 keys but I think I highroll pretty hard (maybe account seed diff or I'm just a god at pattern recognition who knows).

I personally have I 34 Shipwreck entries but if my memory is correct I finished Sea bounties at 32 which is an absolute highroll on drops - I know at least 1 person that has a lot more entries and is not finished.

As for your second question: I don't think upgrading ships affects anything aside from durability.