I have my oil feed line ran from a T fitting on the back of my block to the top of the turbo, and my return from the bottom of my turbo to a fitting that is welded to the oil pan.

The manifold replaces your old exhaust manifold/header. Thats a simple unbolt the old, bolt the new. Then the turbo mounts on that. It can mount in a couple different ways, depending on your manifold (facing up, down, left or right).

If you're running 2 wastegates, sounds like you plan on making big power. If that's the case, you'll most likely need to upgrade the fuel system. (injectors, fuel pump, fuel pressure regulator,etc)

Have you planned out which Engine Management you'll use?