Erick,
Congratulations on your new purchase and welcome to the group! Here's some answers to your questions, I put question marks in some places where others can provide more or better details. I also have a suggestion.
0 - Use the search function on the forum AND on the home page. The one on the home page searches the forum and the Technical Articles. You can find many answers, or at least educate yourself more, before asking your question. I can't emphasize this enough since we have thousands of posts now.
1 - Euro: Some models (280SL only?) had a higher performance cam. Headlights are different. Headrests not required. Seat belts optional (to a later date?). Instruments in metric. Usually no bumper guards on the bumpers. If it's an auto transmission, the Euros commonly had an "Automatic" trunk badge. I've seen an extra chrome strip below the rear license plate for the narrow plates (UK only?).
2 - Major tune up can have many meanings. Are you trying to do preventitive maintenance? Did someone say it needed a "major" tune up? There is an extreamly long list of items you could replace, adjust, inspect, or clean so tell us your main goal first.
3 - Antifreeze is a widely debated topic, just like engine oil. I use standard MB antifreeze that I get at the MB dealer.
4 - There are clock refurbishers, check the vendors database on the home page.
5 - I think I saw someone recommend K&K Mfg. to you on another post. Again, check vendor list.
6 - Vendor list, or e-bay.
7a - First, manuals. I don't know how much maintenance and repair you plan to do yourself. I think all W113 owners should have an owner's manual, the MB Shop Manual (Big Blue Book, or BBB), the MB Spare Parts List book, and the Haynes manual. Even if you don't fix everything yourself, you will be better educated when you talk with your mechanic.
7b - Engine oil? This could be it's own thread. Many people use many types. Traditional, Synthetic Blend, and True Synthetic are all used by various owners. Many different weights are used. I can't recommend anything in particular. Search for oil seal or oil gasket to learn about a key seal often missing fro the filter system. Trans fluid? I think even the manuals use ATF (Automatic Trans Fluid). I can't recommend a brand, whatever MB recommends in the owners manual is probably good. Same with everything else, use the owners manual recommendations unless others here can prove otherwise.
8 - How much does it fluctuate? How hard are you hitting the throttle? I assume this is while you are in gear and the car moves when hitting the throttle.
Sometimes with so many questions it's best to brake them up into their own threads. Easier to manage the information and discussion that way.
Enjoy the new group!!
Rodd
1966 230SL Euro
1994 E420