The stock piping will not bolt up to any 3" exhaust. If you are going to replace the piping, just replace the whole system with a properly suited catback system with 60 mm piping.

As for the turbo route, don't do it because your exhaust is made for it. Even with a small turbo, the exhaust will be overkill. As for your other questions about turbo, do a search as those questions have been covered countless times on this forum.