Hey Jennifer!
Congratulations on planning your first Walt Disney World Resort vacation. You are on the right track with considering a value season for lower crowds and rates.
When you begin choosing a week to travel, you'll want to consider larger events that will impact crowd levels. In some cases, the events may greatly appeal to you and you'll decide to bear a bit larger crowd just to attend. Although events are always subject to change, the marathon weekend will likely take place in January, Epcot International Flower and Garden Festival will take place mid March through Mid May, Star Wars Weekends will likely occur in May/June, Mickey's Not-So-Scary Halloween Party Sept/Oct, International Food and Wine Festival Oct/Nov and all of the holiday celebrations throughout December.
Historically, the lowest Resort Hotel rates will occur January 2nd through mid-February and mid July through September. Holidays and events will raise prices within those timeframes, for example, the Walt Disney World Marathon weekend.
I've traveled within the value seasons several times, however our family's favorite time to visit is early May. We find the weather to be perfect; not too hot, not too cold, with significantly less rain than warmer months. May will be slightly higher in price than earlier or later in the year, but personally I value the chances of better weather over a bit of savings AND the ability to enjoy Epcot's Flower and Garden Festival.
Be sure to keep an eye on the Disney Parks Blog, the independent site mousesavers.com and of course the official
Special Offers page for discounts as your dates approach!