Yes and no. There had been contacts with other cultures for at least 2000 year, however that were the Minoans and Myceneans and those cultures were not yet Greeks. At the year 1100 BC, both cultures had vanished(first the Minoans, some centuries later the Myceneans) and all the contacts with other cultures came to a halt. It's in the time between 1100 and 600 BC the modern Greek culture came into existence with the Gods like Zeus, Hera, Hermes.... It's in this time period that the famous polis-system was developed and as a result of this system, around 600 BC, the old contacts were once again restored.
Technically? Christianity was seen in the time of Jesus as just another branch of Judaism and there were more of those branches. It was never the intention of Jesus to make another religion, especially if you consider that Jesus was a Jew himself.
Judaism is pretty much the Hebrew religion. My knowledge about this is a bit foggy, but Hebrews is a sacred language to the Jews.
You've been discussing about what influenced what. Let me tell christianity has been influenced by a lot of things: Greeks, Romans, Jews, Germans, Celts... actually the christianity we know today looks nothing like the christianity in the time of Jesus.
If you want to have a simple chronology:
-christianity originates from Judaism. It becomes very popular with lowest classes because it has no restrictions on entering(<->Judaism). A lot of Greeks that live in Israel join christianity.
-So the second great influene are indeed the Greeks. Even better, it's because of the Greeks that christianity became seperated from Judaism. It's because it's very important for Jews to cut of the head from there flute(don't know the English word, it's something like circumstanced), but Greeks see this as a violation of the body and refuse this. Because christianity decides that you don't have to do that, they become a religion of there own and are no longer part of Judaism.
-Then comes the Roman period. When Christianity becoms the main religion of the empire, it gets major influences: For the first time there's an official hierarchy, the bible was made etc. You also need to take in account that the Romans itself had a lot of Greek influences.
-In the beginning of the middle ages the church start to convert the barbarians that had overrun the Western Roman Empire. They used a system called "assimilation" for this. It means that they take over elements from the barbarian religions and make them christian. Best examples are the use of old temples and make them into churches and make out of barbarian feasts christian feast(like christmas, according to the bible Jesus was born in march, the 25th december was a very important feast of the Germans).
So as a result a lot of barbarian elements came into christianity.
