well it seems you have planets, 3 tiers of choice based upon your individual talent and decision. Lack of nepotism says they are interested in fairness. It sounds like there is no class distinctions based upon where you decide to be so you probably want to indicate that.
Off the top I'm thinking 3 fields, none higher than the others or at least touching one another so as to indicate if you were high in one you might still be higher than a low individual in another. (By that I mean if you were high up in the guilds you would probably rank higher than a low noble, maybe not in name but in societies eyes I think it would be true). So, if you use triangles make sure that the one on the bottom allows it's highest tip to touch the top of the coat (or similar idea). There is also the significance of the individual and that sounds important based on what you said. So, what if you have 3 fields with circles to imply planets but another circle in the center that overlaps the 3 fields and planets indicating it's up to you. Alternatively you could use spheres instead of triangles with the center section representing the person himself.
The background of a ship named "unassailable" might also play into the coat of arms. After all that is a really strong sounding ship and the people who were on it not only survived by thrived based on what little information you provided. Not sure how you might indicate that, perhaps by color?
I haven't done much of this before so feel free to disregard anything I say. I'm just rambling in the hope that you will get a great idea from it. I do know how to brainstorm. It's not so much what outlandish idea you kick in, it's about the synergy of the group.
So, there you have it, a log on the fire, now is someone will just come along with some gas