Thanks for the input.
I can conclude then that having a new separate monitor would not help very much. I will need something to show me what happens in my current window where my eyes are.
I will look into the GUI settings or some addon to see if I can grey out any characters which becomes out of range, in a way that I will notice.

Maybe see if I can get Jamba to tell me something if they are out of range. I've always used jamba to tell me when any character loses follow, and that was an effective way to keep them controlled. However that doesn't work as well with a melee team which spend most of their time not on follow.

Also I think jamba has the option to display a green/red bar which shows a characters follow status? I could have that enabled and just look at that before I decide to run as a group and pull the next pack.

Also having a star on my main char seems like a decent idea anyhow. I don't always have my camera centered behind my main char, so at times I can start any kind of movement by using the current position of the char, so then it's nice if I know which char to look at