The DLC is separate, I bought the same package and it didn't include it. The DLC/patch will add some new cutscenes to the base game, and for free without buying the DLC you get 2 new keyblades and some new abilities. The new cutscenes might be free too as part of the 1.07 patch. The paid DLC will add new difficulty options to the base game and a photo editing mode, as well as allot of post game content - the main DLC story, 13 boss battles, Secret Episode + boss, etc. I think the only thing you miss out on by not buying the DLC is the new difficulty mode modifiers, which would probably make your first time through more enjoyable - Proud mode is a bit too easy otherwise. Almost everything else is post-game content or it is free with the 1.07 patch.
One thing you do get by buying it now is a pre-order theme that either wont be available later or will cost $.
As for DDD, I just finished it on Normal mode and it seemed about right. Proud would be highly annoying at the end of the game when the boss battles get difficult. I didn't grind in it so I didn't level up many of the high level Dream Eaters as I got them right when the game was about to end.... But if you save the water pinball game for your near end-game Dream Eaters, you can use it to get a ton of skill points to quickly unlock the end-game spells.