I know these things because I research them. It's not hard. Start at Wikipedia and follow the footnotes.

The Arabs who came to the area did not come to an empty land. They came and intermarried with the Palestinians, who were descendents of Jews who never left.

The Jews from Europe spoke European languages, Yiddish and Ladino. Hebrew was artificially recreated at the end of the 19th century by Eliezer Ben-Yehuda.

And no, you can't claim Gaza. The theory that your genes entitle you to steal land is bullshit. Erich Fromm addressed that: "'In general international law, the principle holds true that no citizen loses his property or his rights of citizenship; and the citizenship right is de facto a right to which the Arabs in Israel have much more legitimacy than the Jews. Just because the Arabs fled? Since when is that punishable by confiscation of property, and by being barred from returning to the land on which a people's forefathers have lived for generations? Thus, the claim of the Jews to the land of Israel cannot be a realistic claim. If all nations would suddenly claim territory in which their forefathers had lived two thousand years ago, this world would be a madhouse...I believe that, politically speaking, there is only one solution for Israel, namely, the unilateral acknowledgement of the obligation of the State towards the Arabs—not to use it as a bargaining point, but to acknowledge the complete moral obligation of the Israeli State to its former inhabitants of Palestine"