That's too much of a drop in cals. The lowest you'll want to go is 10-12 cals/lb bw.
Have you done this much ephedrine before? I wouldn't do more than 100mg/day, and even that I consider quite a bit. 50mg/day I have no problem with at all.
I'd switch to moderate carbs. Cardio is fine, so is moderate weight for high reps, if you consider 12-15 high reps (20 for squats). But don't turn your weight workout into cardio, the reason you are working out with weights in this situation is to deplete the muscle of glycogen as well as to signal your body to continue to hold onto the muscle.
As for LOTS of cardio, I'd say no. Look into hiit (high intensity interval training). That's the only way to go for fatburning, imo.