Bringing legions to Rome as part of political struggle had already been common practice for centuries, but it had never fully destroyed the Republic. Caesar himself witnessed several such occasions by Sulla and Marius.
Edit: responding to edit, my point is that Caesar was not fighting to gain. "Crossing the Rubicon" means taking a risk, but I don't think using it to describe creating a startup really fits.
He was fighting (illegally, it might be added) to defend himself against the political tactics of his Senatorial opponents. While he held an Imperium he could not be brought into court for his actions in holding it, but the Senate had voted to make him lay it down. Their intention was to bring him to the courts and ruin him politically and financially. Caesar was simply too proud and too arrogant to allow that ruin; that he was the foremost general of his age meant that he was in a position to pull it off.