On resting in between reps: It varies with the length of the set. 5s or fewer get a breath to reset. Longer sets might take 2 breaths. During the last few reps of a true 20RM squat, just do what Jesus tells you. Trust me, if you do an honest 20 rep program, at some point Jesus will talk to you. On the last day of the program, he asked if he could work in.
