If you're only going to be in Tokyo, forget the JR Rail Pass.
I'd suggest spending at least ONE day outside Tokyo, perhaps two if you can swing it. Different strokes for different folks, though. (Seems a total waste of a trip to spend any time at all at Disneyland, especially if you have less than a week to spend in country.)
Should you plan one more day to your itinerary? That's all up to you. You could spend months here as a tourist and still want for more!