You shouldn't of driven with the plates on the car, why didn't you just get a temp tag from the BMV before you bought the car? Being busy with work isn't going to fly in court I can tell you that. If you say that you're basically telling the judge you were aware it needed attention but were too busy or to lazy and irresponsible to get it done.
If you did use his plates to drive it home you should not have driven it until you got valid tags on it. Is it your first offense? Are you going to have a lawyer?