Man, this is gorgeous and so fitting for Pirate Borg. I also really like the use of the magic square, which is super-atmospheric for something that is otherwise a basic "here's the key to the lock" note. Excellent map as well -- who did it?
Some of the writing is punishingly small, especially if this is printed out at A5. Info about the pregens isn't critical at the table, or Rawlings' quote at the bottom of the first page, but I'd suggest making some hard cuts of the text -- I ended up cutting effectively a whole page from my piece -- so that the good stuff is all legible for the GM.
I would probably cut the pregens entirely, given that there's a good online Pirate Borg character generator that can spit them out with ease. The motives can be assigned without all the space being used on the pregens' stats.
Likewise, I would only print the stats of the new monsters -- which are very cool -- and just use page numbers to the core book otherwise.
10/10 proper names used throughout this. This feels like Jules Verne's Treasure Island. Fantastic flavor generally and very cinematic.