Stage one alternates between A and B. You can do 2 or 3 workouts a week, with 3 being optimal. So, ideally, it would be:
Week one
Workout A
Workout B
Workout A
Week two
Workout B
Workout A
Workout B
etc.
There shouldn't be any reason you can't do your step-ups on the weight bench. Try it! It works great!
See this thread if you are still confused on the Stage 1 workouts:
I must be having a huge brainfart