I am a fairly new player, and I'm trying to understand what would happen with trooper movement on a raised walkway that is very narrow. In this situation the walkway is only 1 model wide. Not all of the troopers would be able to fit within range 1. In this situation, would the trooper who can't fit within range 1 be taken off of the board?

Next question, would anyone recommend terrain like this? Or should the terrain be optimized so that trooper movement is possible on it?

Putting some troopers ahead of the leader and some behind should fit.

Also, cohesion is Speed 1, not Range 1.

I haven't been able to sit down and try it out yet but it looks like I need to sit down with some minis and and the movement template and try it out. I guess I had assumed they wouldn't fit in a straight line from the unit leader

You can exactly put 4 minis behind and 4 in front of a leader (conga line) and still mantain cohesion. So even a full B1 unit would be able to stay in cohesion on a narrow walkway as long as the walkway is long enough.