When coming up with careers, I don't think balance is too much of an issue. Careers shouldn't be balanced, really. Some are far more dangerous than others. Being a marine should be more injurious than being a waitress.
Most of the career flavour comes from the Events table. Make sure that it is unique and that all the events are interesting (so no "nothing happens this term" stuff). Also sprinkle them liberally with allies, contacts, enemies, and rivals. Characters that start with plenty of these are more interesting (and useful for the ref). Events do not need to balance each other. Some could even mean an end to the career without a Mishap, if it suits the career (tho perhaps not at quite the frequency Scouts offers).
If an event requires a skill roll, there should be a reward and a forfeit. Don't have too many +2 to Advancement or +1 to benefit roll, as they're a bit boring.
As an example, the Chancer career in CB2 (gambler, grifter, wheeler-dealer), has many events that gain or lose whole benefits, so that a lucky character could end up with way more benefit rolls than regular. Or none. In contrast, the Secret Police has a tendency to make lots of enemies and even end up a fugitive or in prison.