While I am no exercise guru, I am pretty sure that you could do cardio 6 days a week with no problem. Cardio is actually working your heart. The benefit for people trying to loose weight is that it also burns more calories than if you are sedentary.

Any program you decide to do should be "do-able" in the sense that you need to be able to stick to it and not get too tired and burned out. Design something that you can stick to and you enjoy.

I believe that maximum fat burning benefit occurs in cardio if you can sustain the workout for more than 30 minutes.

Someone feel free to jump in and let me know if I am off base.