It all depends on how much money you are racking in. Remember officiers cost money.
Now i'm currently more familiar with Age of pirates not POTC but as they are similar...
I always had two people on my ship with good pistols and swords plus skills in fighting. They help when boarding other ships as they are much better at fighting then your normal crew.
Other ships I never minded much but if you want them to sail better then it would help to have at least two so you can spread the experience out on them. Make one your boatswain/carpenter and the other your captain/navigator.
Age of pirates uses an officer for each position on the boat (Navigator, boatswain, quartermaster, carpenter, fighter... etc) which makes it easier then POTC but only on the user interface. You will always be able to level someone up quicker on one skill then on many.
So two is better than one but you don't need many as it won't make much differance.
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