Generally, what should I be striving for in chain tension? I read somewhere that (for a fixed gear chain) you can run a straight edge along the hub and crank and the chain should sag a 1/2" below the edge. I did this and my pedals have some play now before the chain catches, is this normal?

Also while I have you people here, I have Shimano slx brake on the front and it has some sort of "quick release" that when clicked, pulls the brakes further apart. Whats the point of this? I assumed to help get the wheel off without messing with the brakes...

thanks!!