I have a stage 1+ Unitronic chip in my 1.8t Jetta, if I put a K04 in would I have to upgrade my software?

the questions are..... having the apr stage 1 tune, would it still get some gains with a ko4? the turbo itself... can you just take a used one off of a stock vehicle? where can i get a decent priced manifold? other than the inlet pipe, what else will i need? do i need outlet pipe...