What ever you like best when you look in the mirror
Depends on what you like. And what your health insurance company thinks. Mine is not very happy with my BMI of 26.
Just ask yourself: Would you like to do that? Is it really too stressful?
If you answer "yes", keep doing it.
Alternate between HIIT and low-impact cardio, though.
Post-workout shake: Good idea. Either Surge or at least whey protein mixed with maltodextrin.
On off-days. 3 days lifting, 3 days cardio seem like a good basic training schedule to me.
But I guess some basic facts would help. So: How much do you eat daily, what amount of calories, what percentage proteins, carbs and fats?
How do you train and how often?