It sounds like you already have enough going on already to support what your goals are, especially since you are already practicing bodyweight exercises. Doing the power/complex lifts once a week will be ok if you just want to throw something into the mix for fun. But if you're main goal is to get better at the sports your doing, then focusing primarily on movements around those sports in place of your workouts will help you see improvements in that area. But to answer your questions:
a) It depends on the loads/volume of the workout and if you are combining the sessions with other workouts during the same day. Doing an intense session that taxes your limits is going to take a toll on your body and be a factor in anything else you're doing that same day.
b) If you put too much on your plate it'l only inhibit what you're trying to accomplish (you want to have ample recovery time from the various activities you're involved in). If you really want to try to work in some strength sessions using weights, I'd say mixing it up week after week. Maybe throw some strength sessions in place of the bodyweight metcons. If strength really is your goal, i'd look at doing more weight sessions than metcons/bodyweight sessions.
"Nobody who ever gave his best regretted it."
-George S. Halas