[quote=@Restalaan]
Hmm, so if say, I want to make a marine character that's starting out like Koby and making their way up. I have to make an entire marine crew of NPC or if there any leeway?

Cause I feel like I wouldn't be able to make an entire NPC crew of a dozen people and RP them well. 
[/quote]

Hillan's pretty much on the nose. I think I understand the mindset you're coming from, in that having a full roster of NPCs fleshed out might help the verisimilitude/feeling of reality, which people tend to like in their stories. But a full ship of seamen is a lot of things you'd have to come up with off the bat. And that ironically it can be constricting too. That's a big part of the reason I deliberately decided not to even think about most of the Warlords/Emperors/Admirals, or even reserve Devil Fruits for NPCs, since I wanted to have room for player input. If you start off with a huge group of NPCs, while this section of the world would be more 'full', it would cut off potentially cool ideas later, or if you didn't like some of your initial ones, it'd be harder to go forward, which defeats the point of all the planning.

What I'd focus on first and foremost is [i]your[/i] character and [i]their[/i] story. You'll probably want at least a small handful to play off of: a commanding officer, a Helmeppo type peer, but they should be in service of your character narratively, be it as a comrade, superior, idol, rival, or some other form of foil. Beyond that, flesh the unit out as you go depending on what your needs are to tell the story of your character, instead of feeling like you have to go all out from the start.