First, pay attention to what section you are posting in. Familiarize yourself with the forum layout and introduce yourself in the appropriate section.

Hold off on the exhaust until you install the Turbo kit. The only significant change by installing one now will be the sound. Plenty of people have installed 3" systems while non Turbo. Might kill some low end power though. Up to you how you want to allocate your funds. 2.5" systems work on Turbo applications just fine.