Hi Samantha!
You picked a great time of year to go. The crowds should be small, except around the Martin Luther King Holiday Weekend. The weather should be cool. Walt Disney World Resort is huge. If you take things easy and take to time to look at all of the details, then you can easily spend 2 days in the Magic Kingdom and 2 days in Epcot. I think 1 day in Disney's Hollywood Studios and 1 day in Disney's Animal Kingdom is enough, though others would disagree with me. You can also visit one of the water parks, though it might be a little chilly to do that; however, the water itself is heated. Finally, you should save some time for a visit to Downtown Disney.
The Park Hopper option really opens up your possibilities. For example, Epcot has some of the better dining compared to the other parks. With the Park Hopper option you could visit any park in the morning and then hop over to Epcot's World Showcase for dinner. That said, however, since it's your first visit, you may not want to leave a park "early". My suggestion is to go without it at first. After you are there, if you think you really would like to visit a second theme park on the same day, then you can always add it on. Likewise, you can add on extra days to your Magic Your Way ticket once you are on property.
Be sure to make an Advanced Dining Reservation (ADR) for at least a couple of Table Service (full service) restaurants. Walt Disney World has some really nice restaurants and it's part of the experience of visiting the resort. Online reservations can be made
here.
Be sure to pick up a copy of the book "The Complete Walt Disney World" by Mike and Julie Neel. It's a great book for first time visitors. It's filled with a lot of beautiful photographs and will give you more of a feel of what there is to do at Walt Disney World.