Hi, Michael!
The various parks of Walt Disney World are far enough apart from one another that, with one exception, the distance is not walkable. (In the case of Epcot and Disney's Hollywood Studios, the walk between the two is about 10 minutes, if you walk briskly.) Take a look at this
Walt Disney World map for a more detailed look at the layout of WDW.
Currently, adding the
Park Hopper Option to your 7-Day Theme Park Tickets will cost you about $59 per ticket. As such, if that additional expense is not an issue, then you'll want to have the option of heading to more than one park per day / night. For example, an early morning breakfast in Epcot might pair nicely with dinner and a viewing of
Wishes nighttime spectacular at Magic Kingdom. Transportation between these two parks is super-easy, so squeezing in a bit more magic is not a hassle at all.
On the other hand, if you'd rather spend that $59 per ticket on food, souvenirs or just save it, there are many ways to plan a tour of Walt Disney World without park hopping. In fact, it's wise to keep your park hopping to a minimum whenever possible, as transportation between some parks can take quite a bit longer than those mentioned above.
In short, if the cost is not a problem, then add Park Hopping; this will give you more flexibility in making your touring plans. If the cost makes you think twice, don't add it. Send me another question and I'll help you create a plan which does not require park hopping at all.
Send more questions as you think of them, Michael; we love to help!