3 roosts would be ideal in your set up (or possibly 2 1/2, nothing says bars have to go across the entire width).
Also keep in mind you want roosts to be above the nest box height. So if you have your nests on floor, then the first roost could be just 1' off the ground. But if your nest boxes...
The answer is: maybe. A ladder set up works for some. Others have their roosts all at one height. Some people use poop boards, some don't.
The important thing is the chickens need to be able to safely land from the roosts (so if top bar is 4' up, they'll need about 4' in front of the bar to...
You have a printer available? You could make a grid and print it out, might even be able to find a grid pattern online that could be tessellated and printed.
Since snow is a thing, even if your plan is to free range most of the time - I'd definitely build the run with at least 10 sq ft per bird, especially since you're not building the coop oversized to compensate for weather (where you build for 6-8 sq ft per bird in coop and/or cull down each fall...