Actually, you are asking three or perhaps four questions here!  The answer for some of your request is solid, whereas, for others it is somewhat more indirect, and, therefore, just might not meet your rather stringent requirement!  You can decide for yourself.

As for the incarnation, there is more than one reference to this in the Hebrew Bible.  But, they are either a bit less direct, or they are ones which some do not accept as being obviously messianic.  For an example of the former, there is Zechariah 11:12-13.  “I told them, ‘If you think it best, give me my pay; but of not, keep it.’  So they paid me thirty pieces of silver. And the Lord said to me, ‘Throw it to the potter’–the handsome price at which they valued me! So I took the thirty pieces of silver, and threw them to the potter at the house of the Lord.”  This is a rather clear-cut messianic prophecy, as it is a reference to giving of a new covenant (v. 10), and it mentions the precise reward given to Judas for his betrayal of Jesus.  The subtle point here is that it is clearly God who is speaking, and God tells us that the thirty pieces of silver were the price at which they priced “me”.  In other words, an incarnate God was priced at thirty pieces of silver.  Then, of course, there is Isaiah 7:14, which describes a maiden who will miraculously be pregnant, stating that this miraculously conceived child will be known as God-with-us.  Is this an explicit teaching?  I would say that it is a teaching that the Messiah will be God-with-us, so I say yes, but some might disagree.  As to the issue that the Hebrew word is not explicitly a reference to a virgin, this is not relevant, actually, as the point is that the child will be God-with-us!  I will mention a third messianic prophecy which spells out the incarnation more clearly.  It is Isaiah 9:1-7.  Here we have God blessing Zebulun and Naphtali, which is the location of Nazareth–on the border between the two.  Then we are told that “to us a child is born, to us a son is given.” This Son will be called “Wonderful Counselor and Mighty God.”  We are also told that “Of the greatness of his government and peace there will be no end.” This “child,” this “son” will take charge of the eternal kingdom of God.  Here we have a clear description of God being incarnated.

As for the idea of an atoning sacrifice, that is a fairly easy one.  I could use more than one reference, but the best, in my opinion, is Isaiah 53.  This is clearly a messianic prophecy (some question this, but this is principally due to their own bias because they do not like the implications of this rather blatant messianic prophecy!).  In this prophecy about the Messiah we are told that “The Lord laid on him the iniquity of us all.”  and that “for the transgression of my people he was punished,” and “the Lord makes his life an offering for sin.”  This is a slam dunk explicit teaching about an atoning sacrifice.

As for your third and fourth request, there are literally dozens of explicit statements in the Torah that salvation will be offered to the Gentiles.  If we can assume that the Gentiles in this case, will remain Gentiles, then they will not be subject to the Law of Moses.  There are so many explicit mentions of this, it is hard to know where to get started.  Let me choose Genesis 12:3 and 22:18 where Abraham is told that all nations, not just the Jews would be blessed through him.  And there is Isaiah 42:6 and 60:3 in which we are told that the Messiah will be a “light to the Gentiles.”  There is an almost unlimited number of explicit statements that in a future time, salvation will be for both Jew and Gentile, but I will let these two be sufficient for now.   You ask for statements that specific commandments such as circumcision will not be required.  There is no specific statement in the Old Testament that circumcision will not be required by Gentiles who come into the kingdom of God.  Here you ask for too much.  If the entire Law of Moses, and if even Jewishness itself is no longer required, then other elements such as circumcision and dietary laws also will no longer be required.  This is fully implied, even if not specifically stated in the multiple passages in the Torah that, in the future, the kingdom of God will be opened to all–to both Jew and Gentile.

John Oakes