I agree about seeing the fireworks that Saturday Night. Its your first night so you can just soak it all up, enjoy the fireworks and then be ready to hit the parks and rides the next day. As somebody said, due to winds and DL being inside a city, its not unheard of that they are cancelled. So at least you increased your chances of seeing those since Remember is only happening on the 18th and 19th of your trip. Had you not come in early, you would have only had one chance to see them your whole trip. And they are so worth seeing! See them by the castle the first night for the full affect, then you can see them back by Its a Small World the next night if you want to avoid some of the crowds that congregate in the hub area.
I so understand your dilemma. Your friends gave you good advice, but like most things regrding a Disney trip, its always subject to change! But I am betting that you'll be glad you had that extra night. No matter how long my trip, I never am ready to go home or never feel like I got enough time.
Have a great trip!