the first phase is exercises of 3 sets of 30 reps trying for near failure at the end of the set. endurance gains are very noticeable. for me about 30% i estimate. i have done the whole twfh and didnt put on any significant weight. but do what you want dood.
with regard to doing mega sets --100+ reps-- friends that did it incurred joint damage cause their form went to shit during the exercise.