I'm late to the Borderlands 2 party, but I picked up the Season Pass for a steal. I'm still only in the teens as far as my level is concerned. However, there are now 3 DLC packs out and I've got them all installed. Sometimes it's tempting to go away from the main quest and just jump into something new and potentially interesting.
In BL1, I played through the DLC between playthroughs of the game, treating the add-ons like continuations of the game post-final-boss. I'm not sure if this is a good idea in BL2 (or even if it was smart in BL1, honestly...)
Is there a recommended level for starting the DLCs? Will I encounter enemies that are too hard if I go early, or too easy if I go late? Are there some weapons or quest rewards that I really can't get the most of until after I'm a certain level?