Mind of tempest
(he/him)advocate for 5e psionics
we could go it is much a ship campaign as it is an underwater setting?I think if you go full water world you can get some really interesting twists beyond "fantasy Caribbean"; ship cities, living islands, merfolk kingdoms, etc. Take every nautical trope from the Odyssey to Horatio Hornblower and smash them all together and I think you could have something cool.
definitely have to move what is in setting important around as against will not work and dwarves just seem daft.
maybe give the less used races a chance to shine?