Expect largely than normal crowds. Remember, this is spring break month across the country, which puts pressure on many entertainment sites. Since Disney obviously attracts children and young people, it stands to reason it would be crowded. Plus, it's in a warm climate; just right for winter-weary folks!
The first two weeks in March have what Disney World calls "average" crowds. You may have some waits, but the crowds are manageable. By the third week of March, spring break crowds are coming and the parks can get pretty full. This is mitigated a bit by longer park hours.
Walt Disney will be too crowded during Spring Break i. e. during the first week of March until mid April, must be present at least 30 minutes prior to shows.
The crowds should be fairly manageable. The kids are in school but watch out for Spring breakers and Northerners who want a little touch of Southern spring. But March is a good month to go.