My personal preference would be to have my vessel determine my career choice rather than my character... allow me to explain:
At the start of the game I opted to sign up for a Navy. I get my first vessel free with basic weapons. As I fight I get limited Gold (to reflect Prize Money), Limited XP (to reflect my time at sea), and admiralty points, as I get more admiralty points I get promoted (in the navy admiralty points = XP) within the navy which grants me a bigger naval crew and larger ships (which I do not own and cannot sell). They have standard guns, so if I want anything special, ie. Long guns, or Modules I have to buy them, but in return my repairs are free.
After a some time, I decide that the Navy life is not for me, so with the small amount of gold I've saved I buy a small trade ship which I own. I buy my own guns and modules etc... and have to pay for my own repairs. In battles I get gold and battle XP (but in most cases I would avoid battles). Instead I would make gold through trading, and gain XP based upon the profit made from buying and selling. The XP would allow me to increase my crew which in turn would allow me to buy & man bigger vessels.
Having done a lot of trading and missing the noise of cannon fire, I opt to buy with my own gold an non-navy combat vessel so I can be a privateer. I have to buy my own guns and modules with my own gold and must pay for my own port repairs. Through battles I earn gold and XP, and the XP allows me to have a larger crew, and the gold allows me to buy bigger non-navy combat ships.
And finally, after all the excitement about being a Privateer I feel slightly hollow, and so wishing to help my country I re-enlist with the Navy, and continue with my past rank and admiralty points.
I thank you for bearing with me whilst I told that rather convoluted and potentially unnecessary story, but I believe that this approach allows a lot of player flexibility.