Don't press on ghouls, they're hard and at one spot there you'll see 4 of them - I couldn't win them on normal (medium). At least not without wasting all of my grog/rum. And it's not worth it yet - they're guarding a high level lockpick chest.
Also there is a grave spider in a cave even harder than those ghouls. I suggest killing all "easy" mobs and skip those hardest ones - you'll return later to that island anyway.
As for "weapon upgrades", you don't need them on that island if you ask me. If you didn't do it yet, just learn the "kick" move.
Cunning boost and thievery 25 is a good option - there is a quest to open a certain chest (difficulty 25 so you'll be able to do it) and if you don't do it while on this island the first time - you'll never be able to do it again.