Forum:Order of Gameplay

A buddy and I have been playing Borderlands on a PS3 the last few weeks. We have faced and killed The Destroyer, and seen the credits, so I suppose we have finished the initial game?

If we continue in Playthrough 1, we get no additional quests, in fact, all the quests have vanished from our screens. Is this normal?

So, where do we go from here? We have the other DLC addons, but are we supposed to go into Playthrough 2 now or procede to the first DLC, which I believe is Dr Ned and the Zombies?

We are both around Level 38 or so. Is this about right?

If you have all the DLC addons, what is the correct order to continue playing the game?