sadly my only strong side in conseption is my imagination , for the ghost it depend wich one we take am not to hot taking those wrapth thingy , they are truly a pain in the boat . But i saw some nice one in the Ivellon donjons that am descusing with the creator if we could get are hand on some of the model he used he also got some skeleton who are actuly not naked!
for the why there undead at this island we could put a crash boat whos is enterely on the beach but fasing the village. for the story something classic from morrowind CORPUSUCT deasise

, the zombie themself could have come from a naufragis that the boat took who was sick , pass away became a zombie infected the other crew member befor dieing , the crew who had aslo pass out when the boat crashed at full speed on the island (big coensidence) have been almost rescu by the people of the town , sadly they were alerdy zombie , the zombie from the ship infected the pop , and now the town is in peiced becose nobody still alive to tak care of everything , so now the land are poison with dead decaid people rotten from place to place , the water suply is curupted with poison also becose of the dead.
the why to go there?
well i got a few option:
-Treasure map from the secret treasor room on your island could bring you there.
-You won a contest and you are now the new governer of the island Harmondale!!!!
-The old freak alchimiste from the emperial controled island got a voodoo scrool who could turn your crew into imortal behing.
-(side effect from sleeping with the wore?)
-You are a mighty pirate and since the navy dont want to help us reclame your land WE NEED YOU TO HELP US
-(you got hired by Umbrella corporation to stop the T-Virus?)
but in all those option the main objectif is to be able to have a undead crew (skeleton one prefered)
am not feeling to hot to put a montain on the island wouldn like to resemble a little bit like the imperial controled island , and i dont know , the water acumulation could come from the montain but i was more thinking of little pone ir and there to give the swampy feeling with big tree that keep the sun from going thrut the brench
i could come up with the raw draw design if you like.