Don’t overthink this exercise.
It is designed as an anti-rotation chassis integrity exercise – the plate on one side of the barbell will try to bend you that way … fight it and stay erect.
Loading & Reps:
5x 1-Sided Dead Lift @ 25# means …
The “25#” refers to the weight of the plate, not the plate plus the barbell. In this case, put a 25# plate on one side of the barbell.
5x = 5x each side. Do 5 reps facing one direction. Step over the bar and turn around, and do 5 reps facing the other direction. Both sides will get work this way.