winter riding is the best. cold crisp air in the lungs! the only thing to stop you from riding is when the trails are snowed covered/ icy. each winter is different in that regard - there are good winters (little snow) and bad winters (trails are out of commission for a month or more). the trails generally are more rideable in central/southern NJ vs. the north.
when conditions are perfect - there is no better time to ride then during a light snow storm. sublime.
as far as gear: you need warm pants (tights), wool socks and warm booties (covers over your shoes). some people get winter shoes but they cost a ton. you'll need a warm upper, gloves and a skull cap (wool cap that an fit under the helmet).
you'll learn from experience how much to wear at different temps (e.g., at 40 degrees, at 30 degrees, at 20 degrees. generally youll find you need to wear less than you think (you dont want to wear too much and sweat too much).
obviously keeping your toes, hands and head warm are the most important. generally, people over-do it by wearing too much on top.
also, dressing in layers is always good, but particularly at first when you dont know how much to wear.
winter rules (as long as the trails are rideable).