Detailed over on the official forums, Marcin Momot made clear what to expect with the newly announced and final piece of free DLC.
What carries over?
Player experience (if you’re below level 30 when finishing the vanilla game, you will be bumped to level 30 for the start of NG+), items (excluding: quest items, books & letters, Gwent cards, usable items, trophies), money and alchemy recipes.
When starting New Game Plus you can select any difficulty level.
You can obtain the Death Match achievement when playing the NG+ mode.
What’s the starting level of the character when beginning NG+?
The same that you had when finishing the game, if above 30, otherwise you start at level 30. You also get a free Clearing Potion at the start so you can reset your skills and try a different build.