Basically, my question was getting at "how easily could one person misbehaving epically screw the entire colony?" or, alternately "How many things to the colonists need to do 'just so' to keep it all viable?"
The more easy for an individual to screw things up for everyone, and the more ways the colonists need to all work together in very specific ways, the more "rigid" the system needs to be, but it should not be a shred more rigid than that.
That's obviously not a complete answer to what sort of government, it's more my initial thought about how one would start thinking things through.
You are now in control of a habitat on the moon. It has no ties to any government; its creation was funded by a wealthy philanthropist who just wants people to emigrate from Earth. The cost of doing so is within the reach of a middle-class family if they sell their home; you can therefore expect a decent number of immigrants.
What sort of government do you establish? How do you go about ruling so that your new settlement on the moon will survive and thrive?