I am a big guy. 5'7' 300lbs(i've actually lost about 20lbs so far). I've been an athlete since I was a kid and have always remained active. I have large developed muscles but the problem is that I habe and an insane amount of fat covering them up.

I do a full body workout 3 X week and I do cardio 5-6 days a week varying the exercises, sets x reps and rest periods in between sets. As far as the cardio goes a walk and jog routine for about 30 minutes on lifting days and for an hour on no lifting days.

My problem is that on lifting days I am spent by the time I start my cardio and I end up doing more walking than jogging. Not only that, I get severe lower leg pain which I think is from poor form and excess weight.

So here are my questions:
1. Would it be okay to do my lifting in the morning and my cardio in the evening?
2. Would brisk walking with varying incline be enough cardio on lifting days if I did it immediately after?
3. Is speed, distance or time more important?

Any feedback would be greatly appreciated.

if you are going to do cardio on lifting days then yes split them up,if you do hiit -cardio that will use up fat during the day by using EPOC "speed up your metabolism" but i would only do HIIT on non weight days yes walking on weights days is ok because weights uses EPOC as well .

so would walking -- jogging be considered HIIT even though it's not high intensity?

no, HIIT is High intensity interval training. So if you do intervals with low intensity, it would be LIIT or just interval training.

As far as the pain from cardio, use an elliptical machine or stair master. It could just be the pounding from jogging is hurting the hell out of your legs. So go for something a little "lower impact".