A: This is a fast growing, interesting market. Wether you can make a living on 3d stock or not is an open, heated debate. If you manage to find your niche market, your models are high quality and you ask a fair price then the thing is usually worth your time.
B: Pirating, torrenting and people selling YOUR models are a widespread issue. The risk is always present. Keep in mind that if you find a paid model of yours on a site for free, then you can ask the site to take it down. Since it's a commercial product they have to comply. Most free models sites aren't into piracy anyway, and pirating commercial products means troubles. Also, many customers pay attention to what they buy/get, becouse buying a pirated model can cause them to be sued and this means a huge money loss.
Anyway, welcome onboard.