As far as the "staging" thing goes, as a layperson I get why the officers would follow those orders instead of running in. In a situation that chaotic, people are acting under incomplete information. It seems possible that as far as those officers knew, there may have been a very good reason why they were told to stage; perhaps they thought there was a team inside, perhaps the gunman was about to burst out of the school and get into a place where he (or they, I don't think the officers knew at the time) could have caused even more damage.
That's what I had thought as well, obviously I know nothing about these types of situations or how to handle them nor am I going to act like I do. But isn't it a somewhat decent reason (even if it sucks to do so)to setup for a second to understand what's going on instead of rushing into the chaotic unknown?
I think this is the same thing with the sheriff, I'd rather hear the decision making and thought process behind the command to set a perimeter before I damn them completely.