I know it is not extremely rare vehicle, but i know it is original and slept very long time. I have all the documents, original spare and tools etc.
Uhhhhh, no, not quite. It's not in the same category as a Bugatti, a gullwing or the car Hitler rode around in, but it's rare enough, has acres of chrome and is unusual enough that you'll get waves, thumbs up, nods and stares. I'm envious of someone starting over with a project car, to be honest
If I can impart one piece of advice, it would be to do research, use the CLassic Center as a last resort, and there's NOTHING wrong with "non Mercedes" parts. Your car is a carb'ed 6 cylinder, right? Mine has the d-jetronic fuel injection system, made by Bosch, and I was given a load of hate and affrontery that I was contemplating using a manifold pressure sensor out of a porsche (both share the same Bosch fuel system). You'll find a ton of aftermarket stuff for sale all over the place, and a lot of us have experience with what might ail you and yours.
If the car were mine, I'd clean out the interior from top to bottom to see if I wanted to replace anything in it. I'd do the same with the exterior, and learn every crease, fold and hazy/grey/rusty spot in the body. Look for rust, if you haven't already and start the plan of attack to get the thing on the road.
Regarding the fuel, again, toss it out in whatever legal way salves your conscience, and make sure ALL the old gas is gone. I wouldn't even use it to see if starter fluid will get the thing cranked over. If your carb is salvageable, crappy gas might end up gumming the thing up.
Once you start needing tech advice, look at the Online Resources portion of the forum - we've posted a ton of tech articles up over the years, and I have more. Let me know if something specific comes up as needed and I'll see about posting it up.
Good luck, drink a beer or two as you get into the thing