And down the rabbit hole we go.
Your story reminds me of......me.
I wanted a clean engine bay, a decent looking body and interior. I even removed enough of the engine peripherals to clean the grease off and paint the engine block while it was still in the car. I discovered that Rustoleum Gloss Ivory was virtually an identical match for my H670 light ivory body color. I sanded the rough spots and used a foam roller to apply the Rustoleum and make the engine bay look like new. I was so proud of my accomplishment. Then, after a while, in the back of my mind, something just did not sit right. Then, like many others before me, the disassembly just did not stop. Now everything had to be perfect. After the body (which was sold to me in 2006 as a rust free car....it was’nt) was stripped and went into the shop for body work and paint. And while the time still escapes me to get it all back together, I do manage an hour here and there to work on it. But I would rather be driving the car.
Anyway, enough about me. Back to your questions. My feeling is that only you can decide how deep you want to go. If you are not sure, get a professional to go through the car and give you an idea of what it takes to make everything right while weighing the balance of restored and original. Personally, original cars are nice but hoses, seals, bushings and fittings age. And don’t get me started of the owner who is proud to display the original spare tire. Even the “Holy Grail” cars who are referenced at MotoringInvestments.com have had paint and certain parts replaced. Does that make the car original? If you spend enough time on this forum, you will find that this subject has been debated extensively.
Plated parts were originally plated with Cadmium. Some shops still do it today. My understanding is that Zinc is now allowed by judges due to the dangers of working with Cadmium.
As far as A/C goes. There is no such thing as original A/C since Mercedes never produced these cars with A/C. Frigiking and Kuehlmeister (manufactured in Texas) were generic kits added on by US dealers after cars arrived in the US. Also been discussed on these forums.
Some people like the Koni’s, some like the original Bilstein’s. Both good products.
You are faced with the dilemma many owners must face when they have a very nice car. Good luck with sorting it all out. It can be part of the joy of ownership.