Passover, without question!
On Sabbaths and Jewish holidays. (The holidays can occur on any day of the week.)
Yes, they often overlap; for example, you may return to prewriting at any time.
I suspect that more Jews have fonder memories of Passover than any other Jewish holy day.
Judaism and Catholicism are distinct religions and do not have any symbols that overlap in terms of both aspect and interpretation.
the Nazis threw the Jews in concentration camp and would punish or kill them for following any of the Jewish holidays or traditions
The first port of call ought to be your local Synagogue, or a Rabbi. Professional advice ought to be available in this way. Alternatively, any Jewish family is likely to have an appropriately marked calendar, and if you ask nicely I'm sure they can tell you how they tend to celebrate the various Jewish holidays.
In 2010, it happens to be the 7th day of Passover. That doesn't mean that it will be in 2011. Jewish holidays aren't tied to the civil calendar in any way.
Jews do not celebrate Christmas because they do not believe Jesus was the Messiah. Hence his birthdate is of no particular significance to them.
Yes. However, there's a custom not to do any time-consuming work while the Hanukkah-candles are burning.
Yes, Shintoism has holidays.
Most religiously observant Jews will not attend any service held in a Christian church. Depending on the Jewish holiday, most Jews, of any observance level, would not attend a service held in a Christian church.