I've found what may be contradictory statements, so I'm looking for some clarity.
It looks like Careers are part of the path, so you can select what class you want to be if you start from the bottom down. Or do you start at the motivation instead and just pick your career? But then chart 1-1 says careers can be from any homeworld, but gives examples of norms. If you use the chart with the careers, Rogue traders can't be from death worlds and astropaths can't be noble born, the chart just doesn't reach that far.
So are the careers part of the path or are they an open choice?