Some ideas on how each player can contribute to building a world. It's all about relationships and broad strokes that the GM or players can fill in the details of at a later date-
Genre of Airship Pirates I view as swashbuckling therefore, each player could do the following-
Plot
Who is your Arch Nemesis or Main Rival? Why?
Name at least three people you hate and why.
Name at least three people you admire or love and why.
There are 50 crew - establish relationships of some sort with at least 3 of them (not including any complications you already have) - this also means naming them. Ideally name them without consulting other players - I'm keen on getting rid of the media trope that every NPC must have a unique name

Colour
Invent a religion (it's post-apoc and it's America, they would have millions of new religions). Maybe just a couple of sentences - and whether it was something your character heard of, knew someone in or actually was a member of.
Name a rival pirate ship and/or crew. If enthused, write up what they're famous for.
Invent a fantastical steampunk machine and your relationship to it. You saw it, had a friend die building it, aspire to steal or build one etc.
PC vs PC
Establish at least two relationships between your PC and every other PC. Maybe something like “owes $10 for a bad wager in a dog fight last month” or “has been secretly short changing them when buying supplies for the past year in order to buy drugs”
Make up 5 aspects (short descriptive sentences) for your PC, and show them to the other PCs - Other PCs should prioritise them, add or subtract aspects, and write down the results for how their own PC views your PC.