March can be a busy time, due to nationwide variances of spring break. If your trip falls within the first two weeks of the month, though, crowds will likely be very manageable.
Disney publishes a calendar that may be able to help you (and other crowd-avoiding guests) decide when the best time to vacation is. They base their recommendations on low rates, low projected crowd levels, and comfortable weather. You can take a peek at the calendar by clicking
here.
As for special events in early March, I'm afraid you're out of luck. The flower and garden festival at Epcot doesn't officially begin until the middle of the month. The good news, though, is that the closer to the start date (March 18th) you visit, the more likely you'll be to start seeing special floral displays pop up as Disney's talented horticulturists prepare for the big event.