I'm sorry to hear that.
Where did you get these hens and did you quarantine at all?
Unfortunately, many respiratory illnesses are viruses and are sometimes treatable but incurable so they birds will be carriers for life.
Do they smell funny? Any swollen eyes?
Steps are easier in many ways.
Ideally, you should have the equivalent of 1 sq foot of permanent ventilation per bird, I dont think you'll have enough with your current plan.
I'd just add a stump for a step, or no step at all for two feet.
You want your roosts above the nest boxes but below ventilation , what type of ventilation do you have?
Any more, people seem to feel explaining all the ingredients is necessary and it's annoying.
I know what salt is.
I know what salt is for.
If you can't figure that out, I don't want you near the kitchen.