Though the charges were dismissed your record will reveal that you were arrested and charged, but that the charge was dismissed due to your completion of the program that you had to complete. In fact the FBI will be able to access even expunged convictions. If the application asks about convictions only than, yes, you can answer truthfully that you do not have any convictions. However, they may ask about charges; if they do you will have to answer yes. Lastly, I do not know whether or not a dismissed DUI charge from two or more years ago would preclude you from security clearance. It might put a couple of speed bumps in the process, and be cause for a little more inquiry, including a substance abuse assessment to determine whether or not there are any ongoing problems. What I will tell you for certain is that lying or covering up anything at this phase that is later discovered will certainly crush your efforts and goals.
Public defenders start at about $52K and can earn over $150K after they've put in a significant number of years. Many private criminal defense lawyer's practice consist in large part of court-appointed cases. They get on a panel and should generally make $100K-$200K with a few years experience. Others have a flourishing practice, filled primarily of privately-retained clients and make far more. As with any other profession, how much you make is also a function of how important money is to you. The more you want to make, the more your career decision will be driven by meeting that goal.
My advice is choose the area or law that excites you most and has personal meaning for you. It's a great feeling to get up everyday and look forward to work.
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