We just returned from an end of March trip and the crowds were definitely there - but managable with a plan such as Tour Guide Mike. The weather was perfect - sunny, 80's, not humid at all.
I live in middle Georgia and I know humidity. I would NEVER go to Disney during the humid late summer. Even our last couple of days, when the temps reached mid 80's, I made the comment to DH that that was as hot as I would ever want to do Disney.
Don't be scared of the crowds unless Easter falls the week before or after you are planning. We had plenty of Spring Break folks and still did everything we wanted and even more. We will definitely go at this time again.