Can there be any difference between eating a high calorie item at one meal, or spreading the calories out?

Yes. Excessive calories at one meal can't be fully utilized by the body in the short term and will need to be stored.It is therefore preferable to consume 1500 calorie over several small meals(4-5 meals avg ~300-350 cal/meal) vs. One meal of 1500 cal.A smaller meal is a more efficient way to burn the calories that you consume, as the body is able to utilize smaller calorie loads in a short time.
YES. Eating a high calorie meal can lead to higher Insulin levels with a crash afterwards that causes hypoglycemia. It is better to eat smaller meals more frequently to level the highs and lows that over the years will lead to Insulin resistance and adult onset diabetes and the problems that go along with this.