Hi,
1. Are all Orthodox, Eastern Orthodox? Or is the Eastern Orthodox Church the largest.
Orthodox Ecclesiology is quite complex and it is very hard to compare with Catholic Ecclesiology.
If you want to find a single institutional organization called "The Orthodox Church" that you can compare to "The Catholic Church", then Good Luck, I haven't found one.
The term "Eastern Orthodox" refers to the various Churches of Byzantine tradition that accept the (first) 7 Ecumenical Councils in their matter and form.
These Churches are not all in full communion with each other, although all will recognize the others as Orthodox.
They generally regard the Ecumenical Patriarch of Constantinople as "First among Equals", but that doesn' give him any jurisdictional authority over all the Eastern Orthodox.
Then you have the Oriental Orthodox, which are the Churches that accept only the first 3 Ecumenical Councils in matter and form. They are mostly in communion with each other, but not with the Eastern Orthodox, and there is no jurisdictional relationship between them whatsoever.
Some Eastern Orthodox regard the Oriental Orthodox as orthodox, or at least almost, but there are other Eastern Orthodox who regard the Oriental Orthodox as heretics.
Yes, there are more Eastern Orthodox than Oriental Orthodox, and the largest Eastern Orthodox Church (the Patriarchate of Moscow) is the largest Orthodox body of them all.
In addition to these two "families" of Orthodox Churches, you also have the Assyrian Church of the East. They accept only the first two Ecumenical Councils in matter and form, and they do not style themselves as Orthodox, but the Catholic Church regards them, together with the Churches of both Orthodox families as true Particular Churches, with fully valid sacraments.
The Catholic Church and several of the Eastern Churches have issued common Theological and Christological statements meaning that, although some of these Eastern Churches do not accept the formulations of all (the first) 7 Ecumenical Councils, at least some of them have "compatible" Theology and Christology.
Many Eastern Orthodox regard this "compatibility" irrelevant, they require full adherence to the matter AND the form of the declarations of the (first) 7 Ecumencial Councils.
2. I have read that it may come easier to have full communion with the Oriental Churches first over the EOC? True?
Hard to say for sure, but I generally agree with this assment.
3. Could an EOC like the Antiochen come into full communion with Rome without the approval of the Pat. of Const. ?
Yes, they could, and it has happened before in the case of most Eastern Catholic Churches.
None of the parties involved favor this kind of process any more, though.
Shalom,
Memo