If I play Point Lookout will all of my stuff (weapons, armor, followers, stimpaks, caps) come with me or do they stay in the Capital Wasteland? I have a bunch of awesome equipment, two companions, and more caps than I know what to do with. Will I be able to use them in Point Lookout or only the Wasteland?
You don't lose anything when you go to Point Lookout, you continue to use all your gear - it's just another area you can go to. Like the other DLC-only regions, however, your companions will not accompany you to Point Lookout, but you can find them back in their "home area" when you return.
If you don't care about spoilers, here is where you can find the list of possible companions, and you can click one of them to see where they go to when you embark on a DLC area.