Other Than Warming up......

I'm back at the gym after several years. I'm 6'5" 210lbs(dropped 7 pounds this week), meduim frame. In the past I worked out and dammit if I had a killer of a time to gain weight, I realize that my diet probably wasn't up to par but my I'm the type of person that can sit and eat buckets of pasta 7 days a week and not gain an ounce(my wife hates me for that lol).
My question(s) are.......Other than a part of the warm-up should I be adding a cardio routine to my workout? Does cardio for a metablolism like mine affect gains negatively? And finally, if yes I need to add cardio....how often and how long should I tread, bike etc...?

Seperate cardio from your workouts.

If you have a hard time gaining weight you shouldn't worry about cardio.