What's your opinion of HIIT vs steady state cardio? Why would you do one over the other and what time of the day do you believe is optimal?

I'm a 14yr stage 4 testicular cancer survivor having problems making gains. My diet is clean and I make sure I get enough protein, carbs, and healthy fats(try to anyway). I have low T and cortisol issues that I have a Dr  appt for on June 16. I had half my right lung removed because the cancer had spread and my Dr wants me doing cardio for 30 mins 5 days a week. Is it at all possible to put on lean muscle while stil pushing myself as hard as I possibly can and having to do this much cardio? Any help is greatly appreciated! Thanks Marc.

How important is or how important do you feel is stretching before, during, during sets or post workout?

I am wondering if it is really beneficial double or even triple scooping your Protein Powder after working out. 

Lot of people I know take 2-3 scoops of Protein Powder post-workout. 

Is it not too much at once? 

And can your body really absorb all the protein or are you just consuming unnecessary calories and wasting your money?