Wow, 120lbs is major!
I lost about 100lbs with the Atkins diet five years ago or so and have kept most of it off (I need to drop about 20- winter is a tough time to stay active in South Dakota).
It will be very important to ease back into eating, that's for sure. When the caloric intake drops to that low a level it triggers the 'starvation response,' drastically cutting metabolism. So when you go back to eating even 2/3 what you did before the weight comes roaring back. It's smart that the diet takes this into account and adds food back slowly, giving the metabolism time to adjust.
Good luck with your program and welcome to DC1