Based on crime statistics, it seems the odds of lethal weapons being used is relatively low, but you definitely want to be prepared to handle such encounters before you begin crime patrols. Calming a situation with threat potential is preferable to having to fight to stop a threat.
As for armor, ballistic vest and padding are a good place to start. If you're not going straight into crime patrols, then start with a good set of pads (I know you are on a budget at 17), but only after you have had training.
Honestly, I wouldn't advise anyone to patrol without proper gear, but I understand you are not just jumping straight into the lion's den. The clean up you posted about earlier will not require such equipment, and the longer you work on that mission, the more time you will have to train and save up for the "good stuff".