Hi, Julia!
With careful planning, your son's first trip will be absolutely magical, one both he and you will never forget.
Let's get started!
First, take a look at the park calendars to see if there are any
special events you'd like to experience while in Walt Disney World. For example, in the spring, you can visit during Epcot International Flower & Garden Festival while in May, Stars Wars Weekends take place at Disney's Hollywood Studios. In the fall, you'll find the Epcot International Wine & Food Festival. Take a look at your options, since you have yet to set your dates, and pick the one that's most exciting for your family.
Next, select your resort. Determine what's right for your budget by plugging some of those dates into WDW's online reservation system. Just click on "Book Your Vacation" from the main page. You won't have to reserve just yet, but this is a great way to explore your options and get a better idea of the amenities and costs of each resort.
Once that is finalized, you can begin to plan each day of your trip, with dining reservations selected, in part, based on park hours and events.
Regarding flying versus driving? We've done both, so I have to say that it depends on your particular needs at that time. Unless you have a reason to want to drive your own car from Indiana, with a carload of supplies, it might actually be easier and more cost effective to fly. (Those tanks of gas really add up!)
Send more questions regarding packing tips, resorts, dining options and planning; I'd love to help!