Like Njayminsim1115 said, it might already be set up for you. The devs likely have a system in place, and they will decide who becomes the Captains and CoP. Not just one person. From 2 and a half ears experience with Asylum Life and over a year being an officer in their Arma 3 servers and currently Corporal rank (which is the first rank that you have to pass a vote to get), I can tell you the system is not perfect but it's good for what it is and has a Chain of Command for promotions and such, not just on guy picking everyone. Plus CoP is decided by the admin team. I assume that in general, with adjustments for what new things the game has to offer, they will probably use the same general structure. Plus my guess is that, along with some people from this community, they'll probably get people they already know can handle the positions from Arma 3 to fill their positions.
However, that being said, note that I said "I assume" and "my guess" and "probably", because in reality no one except the devs know what the system will be like and it could be completely different from Arma 3. I'm only using what I know from experience on their Arma 3 Asylum Life servers. I just don't want people to get ahead of themselves and find it ends up being completely different.
Im all for proposing ideas for what it COULD be like, just know that doesn't means that that's going to be what it WILL be like.