Time to close the quiz. Here are the answers:
Group 1:
1 -
Lewis chessmen, ~12th century, Scotland. I was surprised with how many people knew these!
2 -
folding screen, namban art depicting an arrival of portuguese traders in Japan, 16th century, Japan.
3 - greco-buddhist art,
indo-corinthian capital from the Butkara Stupa, ~1nd century BC, Pakistan.Interesting how two types of art apparently so different merged for centuries.
4 - Eastern Zhou Dynasty
bird shaped bronze wine server, ~5th century BC, China. I admit, this one was in to deceive people as a Benin bronze.
5 -
ivory salt shaker, 16th century, Benin. These, and other tableware (spoons, forks, etc) and statuary were produced for export to Europe, incorporating european themes which the sculptor probably had never seen personally. I was fascinated by these and other african pieces I saw recently on a museum. Hoped that the ivory would be noticeable and a good hint about its african origin but the replies placed it all over the world!
6 -
Farnese cup, a libation plate sculpted in sardonyx depicting either gods of members of the ptolemaic ruling family as gods, ~2nd century BC, Egypt. Saw an image of it on a book cover and was immediately fascinated with the detail on such an ancient work.
7 -
Mayan codex known as Dresden Codex, ~12th century, Mexico (probably).
8 -
Medici porcelain, 16th century, Italy. This was an early attempt at producing porcelain in Europe, financed by the Medici family, but the quality was inferior to the chinese products and the enterprise collapsed as sea trade with China increased.
I've accepted any answer which was "close enough" in time or function/description of the object. This kind of questions are not easy to evaluate, but I find questions using images more interesting.
Group 2:
1 -
Arthur Wellesley, 1st duke of Wellington
2 - Klemens Wenzel, Prince von
Metternich
3 -
Feodor Kuzmich/Alexander I of Russia
4 - Charles Maurice de
Talleyrand-Périgord
5 -
Wilhelm von Humboldt
Four of them certainly met, as the negotiators from the main powers of Europe, at the Congress of Vienna to remake the political map of Europe (depicted on the background in the coin with the portrait of Metternich). The one which may or may not have been there is Feodor Kuzmich. There is a legend and some speculation identifying him with a retired Alexander I, but no definitive proof.
Group 3:
Here's what I ended up accepting for each individual. Answers within a couple of centuries of their lifespan were fine for the ancient ones.
This question became somewhat embarrassing for me as I found out from the answers that some of these people supported other ideas I wasn't aware of.

And that the dates I initially had for Confucius were wrong (+1p for dragonlord)!
Diogenes (494-323 BC), Turkey, Greece cynicism
Jean Meslier 1664 1729), France - atheism
Jacques Roux (1752 - 1794), France - anarchism, direct democracy
Henry David Thoreau (1817 1862), USA civil disobediance
Jean Bodin (1530 1596), France divine right of kings
Jean-Jacques Rousseau (1712 1778), Switzerland - direct democracy
Thomas Hobbes (5 April 1588 4 December 1679), England monarchism
Lucretius (9955 BC), Rome agnosticism
Pierre-Joseph Proudhon (1809 1865), France mutualism, anarchism, socialism
Saint-Simon, France (1760-1825) meritocracy, socialism
Robert Owen (17711858), UK/Wales socialism, mutualism, atheism
Confucius (~551 BCE 479 BCE), China meritocracy
Final Score:
civ_king and Yeekim, 39 points.
Tabster, 36p.
Sydhe, 23p.
Redy, 22p.
Dragonlord, 20p.
Taliesin, 19p.
Do we have any rule for tie-breaking?