I was at WDW during early March in 2002. Crowds were fairly light and we got right on most rides in the theme parks. Remember, this was just a few months after 9/11, so my experience may have been skewed.
Temperatures when we first got to WDW dropped into the upper 40's at night and the 60's during the day. However, by the end of the week that year the temps climbed into the lower 80's during the day.