[@Scarescrow]
Oh, it looked like you just said "Interested"
Well, basically:
>What are the positions presented on the pirate boat?
One Piece crews don't resemble real life naval crews in the slightest, so you can be whatever you like! Oh, but you probably shouldn't be a computer programmer, unless you plan to invent the computer.
>How many skills are we allow to pick in the beginning?
Up to eight points of skills! Of course, if your character knows how to do something and just isn't very good at it, you can write it up as a skill with 0 ranks.
>Are there any scale of power as some of the characters in the story could literally blast an island into nothingness? 
Sure, all you need is to become a high-ranking marine and issue a Buster Call! Word of warning: This is generally considered "not cool", and may put you at odds with your fellow players.
>Would Haki count as a skill or a "superior skill"?
Technically, each individual type of Haki would be classed as it's own superior skill, but that's mostly a semantics question because nobody in the first half of the Grand Line uses Haki to begin with. Frankly, even within the confines of the story it felt like it went against the core points of the setting and was forced in purely to nerf logia-type fruitmen, so I don't think it'll ever come up in this game.