With the personnel, you get some when you first unlock the harbor. You will get more as you move through the tech tree. Each comes with stats that are either buffs or debuffs to your Promethium-gathering ship. When you pick a person, they become a crew and gain experience which will improve the stats they come with. The goal is to get as much promethium per journey as possible with as little sacrifice as possible so picking the right ones will be a little puzzle for you.
You can check the wiki to see how some of the crew evolves in stats, but the information is uneven for all of the crew so you may have to just go with what you know.