my goal is maintain or increase my leanness and gain lean muscle mass. My question, how often should I work out a muscle group per week and how long so I may accomplish my goal.

It's always good to change things up and you can seriously workout a muscle about every 72 hours, so that could put it in the 2X per week.

Strange enough, I have heard some Olympic lifters training legs 6X per week. So, a lot will depend on nutrition, rest and type of work you do.

Winter time, I tend to do 3X per week workouts doing full body. This season, I'm going to incorporate more cardio whereas previous times, there was...NONE.

Thanks for the advice man. I've heard different opinions on frequency so I'm just trying to help clerify it a bit more.