I sold my motor to a friend about a year ago. I let him do payments (my mistake

), and we wrote it all down on a contract. He was to do $500 payments each month. After 2 months, he stopped paying, now I want to take him to small claims court. (BTW he took the motor when he signed the contract, so it's no longer in my possession) My question is, how can I prove he didn't pay? Or is the burden to show proof that he paid (i.e. returned checks) on him? I know I am the one obligated to show proof that he owes me money (which is the contract).
Another question is, I don't have his current address, because he keeps moving, but I know where his parents live, and he frequently goes there maybe once a week. I call his old residence and the people there (his in laws) won't give me his phone # or new address. Can I just use his parents address to file the claim?
Last, what if he doesn't pay? I know he has NO assets whatsoever. He just sold his car, and he has nothing else. Maybe a Playstation or something. How can I get him to pay if he has no money?
Oh one more thing, I was planning on recording a conversation with him (without his knowledge) in case he decides to say he paid me off and deny he owes me anything, is this illegal? I think it is but I just wanted to make sure. I want to be as prepared as possible to go to court, need all the help I can get. If anyone has the answer to these questions, please post! Or if you have any tips from experience. Thanks guys