Gloria cuts her left hand open with a knife, yet is later seen to be uninjured as she is playing the cello. Additionally, when the cut is shown being made, she is using the dull side of the knife.
When Phil and Monica are talking about the money and she wants half, the bridge behind Phil changes in both color and style. The first bridge shown is a dark through arch bridge, then a lighter colored suspension bridge is seen, and then it reverts back to the through arch bridge. This indicates the shots were done at different times and locations. The through arch bridge is later seen when Gloria is jogging.
When Phil is shredding papers in his office, depending upon the camera angle the bridge in the background out the window is close and then far away.
Antifreeze does not come in small bottles as was shown, and would not need to be ordered through the mail, it can be purchased locally at any number of stores.
The small amount of antifreeze consumed by Monica would not have been fatal.
When Kim is shot, red stains appear on her dress immediately. Bullet wounds do not result in that happening, the effect was a dye pack being exploded on the actress.
Poisoning by ethylene glycol (antifreeze) is cumulative over time and would not result in an instant death as Phil was relying upon. It would take the direct consumption of several ounces for a dose to be fatal, and at that it would take several days.