Refitting DTS

I have a beautiful 2001 DTS and will not part with the body style. I have tried to like the new DTS body style more than mine without success. So I've decided to get new working parts. Please tell me where to start and which parts probably need to be replaced. I know I will replace the engine (150,000 miles) and OnStar. Please point me in the right direction to begin this process.

Welcome to AF, this is an impossible question to answer, how would we know what parts are worn out enough to require replacement, some has to go over the car completely to see what is required, don't discount the engine without a proper analysis.