Whatever level your character was when the DLC was installed was the level for all DLC items, difficulty, etc.
I am not a beginner to Skyrim by any means, but I have never installed any of the DLC before.
Thanks for any information.
Nope! The DLC levels just like everything else in the game levels and is completely independent from whatever level you are when you install them. Though I'm pretty sure they have level requirements, like Dawnguard starts at level 10 and Hearthfire at level 8 (or 9?).