Coffinworm 5/3/1

Hello,

Is this okay to do backdown sets after top set for the coffinworm leader template?

Can you do all push assistance work (100-200 reps which would be the week total if you do 25-50 reps x4 days) on bench day for example, pull assistance on deadlift, single leg/core assistance on squat or DL?

Thank you!