I just looked that up (Luke 10:1) and it varies by translation. NIV, NLT, etc, have “seventy-two” while NCV, WEB, KJV, etc, have “seventy,” and so on.
There is a fellow named Crescens who appears in the New Testament.
Apostolic Constitutions (375-380 AD), VII 46, lists him as a Bishop of Galatia, so you’re right.
There is a difference between the Eastern Catholic rites (like the Byzantine, Marionite, etc) and the Eastern Orthodox Church. The Eastern Catholics are in communion with Rome, while the Eastern Orthodox are not.
Yes, there are differences, the most important probably being that they deny papal primacy as Catholics know it. While us Western Christians often downplay it, the filioque is often cited as a large issue. Original sin vs ancestral sin. Energies vs essence (are they the same?). The intermediate state (Purgatory or something else?).There is more
(read here), but the point is that both Orthodox and Catholic Christians are part of a wider Christianity.