For those who asked about vocals legibility...
I used a 24" LCD front and center. Sounds small compared to the 42" displays I've read and seen here, but mine is propped about waist high so it sits closer to the singer's eyes. Guitar players are looking at relatively large colored blocks so they aren't as concerned about the sizing on the screen.
For larger setups I have an individual screen for each performer, but for smaller stages even though I might be able to fit them, I stay with just two otherwise people are cramped and cannot move around freely.
You can see them in our videos:
Has anyone found that the scrolling text mode is better?
I've been tempted to try it or give the option for Karaoke veterans, but once you try the right to left moving mode it's hard to try the scrolling mode...at least for me.