Hi there, Amber!
March in Florida is glorious. The weather is generally dry and warm, with day temperatures in the mid-80s, and nights in the high 70s/low 60s. The humidity is practically non-existent, too. Swimming is definitely on the table, since every pool at Walt Disney World is heated to a comfortable temperature based on the outside air.
Because March typically encompasses Spring Break for lots of the country, it is considered "Peak season" (from March 9 - 31). Thus, the number of promotions are relatively scarce. The
free dining plan that's being offered right now, for example, is good for stays in the future: from August 25 - September 29, 2012, to be exact.
Your best bet is to check in periodically with the
Special Offers page, and see what might pop up as your personal booking window grows near.
Have a wonderful time!
See you later, celebrator,
-Deborah B.