they don't care what you have done in the past for DV (within reason), just be open and honest and tell them everything, a few splifs as a student and trip to red light district is no big deal, just tell them (and don't do it again of course). Just be prepared to tell them about all your private, er, 'hobbies'. They are looking to see if you are honest and trustworthy, they are not looking for you to be a monk.