Hello, Robin!
You are absolutely right to plan ahead and not miss
IllumiNations: Reflections of Earth on your upcoming trip to Walt Disney World.
Since you'll be in the parks in March,
check out the March calendar for Epcot. If IllumiNations is scheduled for a 9:00 p.m. showing, I suggest that you arrive at a location with a great view of World Showcase Lagoon. Personally, I prefer to be on the side of the lagoon that is closer to the attractions of Future World, so that if we are exiting right after IllumiNations finishes, we're that much closer to the park exit. However, if you are a Walt Disney World Resort guest, and are planning on taking advantage of evening Extra Magic Hours on your night in Epcot, then there are several terraces in various pavilions in the World Showcase that offer lovely views as well. Any location with a water view will afford you a great vantage point; just consider what will be easiest for you to get to, and to your next stop, when the show is over.
As you wander the park that day, keep an eye out for a location that will be convenient based on your evening plans. Then, about 45 minutes prior to show time, arrive at your preferred location and relax until the show begins. You might want to grab a special snack or beverage en route so that you've got all you need, as well.
I'm sure you'll have a magical time as you view this spectacular pyrotechnical display. Please send any additional questions you may have you plan your upcoming trip! I'd love to help!