Chris's involvement with...(SPOILERS)

#1: It wasn't glass. It was red food coloring that failed to break down in the stomach and when a few coincidentally sick kids vomited, it came back up red. It wasn't sabotage, it was simply a bad batch of food coloring that unfortunately caused a scare. You need to watch the movie again if you are confused on such a basic and clearly explained point. You must have fallen asleep.

#2: Many of the plot devices are either not explained or else implausible. For instance the bee killing Platt. One explanation is that Kris was a witch with magical powers.

#3: Yes you are supposed to suspect that Peter still has paranoia issues. This issue is meant to be ambivalent until the final scene of the movie.

#4: You are right about the "so what" factor. As has been pointed out many times in the user reviews, the ending of the movie seems made up on the spot. The trivia section mentions that studio brass imposed an alternate ending on the director, perhaps at Dunaway's insistence.

#5: Very little in this movie makes sense. It may be fun to examine the plot holes and bring them up for discussion (we can never get enough "The Temp," so let's leverage cyberspace to get more visceral enjoyment) but don't expect to squeeze any plausibility out of this script.