The largest services fall in the High Holy Days. Rosh Hashanna, the New Year, usually falls sometime in late September-early October. The most attended service is Yom Kippur, the Day of Atonement. It falls ten days after Rosh Hashanna.
The Great Belz Synagogue in Jerusalem is likely the biggest Jewish synagogue in the world currently.
American Jewish World Service was created in 1985.
I'm not sure what you mean by a "big" Jewish service. -- Longest service: Probably the Musaf service for Yom Kippur. -- Most heavily attended service: Tie between Kol Nidrei and N'ilah services on Yom Kippur. -- Most important service: All are tied for first place, i.e., if there's any one service that's more important than any other one, we don't know it.
Jewish (75%).
God.
The rabbis in Israel.
A Rabbi
Probably in London, England.
The stand in which a Jewish Cantor (someone who leads a Jewish service) rests the Torah on.
In the morning service for weekdays, as well as in the Sabbath and Festivals morning service.
It's an additional Jewish service.
Any Jewish male who is more than 12 years old, has no gross physical deformity, and does not have a non-Jewish spouse, can lead the service. A rabbi is not required to lead any part of the service, or even to be present during the service.