[MENTION=51930]fireinthedust[/MENTION]- Since multiclassing is back (to some extent) and the proficiency bonus makes it so that specialization is less crippling than in previous editions, it’s a lot more viable to have a multiclass wizard who’s also a capable warrior. For example, you could go with a fighter 1/wizard 3 (abjuration), take true strike, mage armor, and misty step, and say you’re off to a pretty decent start.
...Or a warlock with the pact of the blade. That also works.
A pact with Davy Jones/Dagon or Calypso/Cthulhu? Swashbuckling pirates are probably not going to have Lovecraft’s twin-pronged phobias of...nearly everything, so the loathsome Deep Ones are actually the beauteous Mer (possibly conflated with the sahuagan or kuo-toa), and a pact with an old sea god isn’t quite so terrible...if you’re a would-be pirate, at least, committing his daily tribute to the depths.
I for one still like the idea of the callow youth making his way in the world, which does sort of seem at odds with vampirism and elder gods.