OBDII Turbo Question

[E36Bmer]

I am considering building a turbo kit, but have a couple questions. What is the Air Pump? What does it do? Do I need it, and how do I get rid of it, just basically, what do I do about it b/c it looks as though i will not have any room for it after putting on the turbo manifold.
I have noticed that almost everyone has on-center turbine housings, Does anyone know if a small tangial turbo such as a t3/t04e .60a/r will fit on a turbonetics manifold, as in space, I already know the flange will fit. I just don't really want an on-center turbo, they are less efficient and harder to find.