You're complete right, diet's the main factor. Get that dialed in first, as it sounds like you are doing. And dial it in specifically for your needs. That is, "paleo" is a very broad category when juxtaposed against "50 pounds weight loss goal." For instance, nuts are paleo and nuts are calorically dense.
As for cardio: you are more likely to get the cortisol levels too high from spending time doing lots of low intensity cardio: high-volume, mid-range "jogging-type" activity. (I don't include walking in this category.) Focus your cardio on HIIT: keep sessions intense and short, ideally on days other than your heavy liftIng. If same day, space HIIT several hours apart from lifting.
If losing fat is as important as losing 50 calories per se, the right diet-lifting combo can nail the goal, without significant emphasis on cardio. Doing to kinds of heavy lifting you're doing, and then adding lots of slow, low-intensity running (for instance) is typically a recipe for burnout. Better to rest and let your powerful diet-lifting combo achieve its effects.
Consider taking a look at leanfit.com. Powerful results with specific timing of eating/not eating. Minimal emphasis on cardio. The approach there isn't for everybody. Get to know his concepts (for instance, fasted training) and see if they might apply to your goals.
Don't undervalue walking, especially in a fasted state. You'll lose pounds. But don't make the mistake of thinking, "Hey, I'll lose even more by stepping up the pace and jogging fasted. That could up cortisol, slowing weight loss.
