You are going to need to upgrade your fuel setup if you plan on running a bigger turbo.
If you are looking to a t3/t4 hotside you will most likely want to upgrade your exhaust manifold. They do make adapter plates for the stock exhaust manifold and t3 setups. Which is alot cheaper than a new manifold. They don't flow as well as a equal length though.
It all really depends on your goals. What kind of power do you want? What are you using the car for?