What are common things that both Orthodox, Roman Catholic and Protestants agree on ? I have a little list. Feel free to add:
1. The Holy Trinity
2. The Virgin Birth
3. The Divinity of The Lord Jesus Christ and The Holy Spirit.
4. The Old Testament Prophesies of Jesus in the Old Testament.
5. The Nicene Creed
You have independently arrived at a partial reconstruction of the Chicago-Lambeth Quadrilateral:
In the opinion of this Conference [i.e. the Lambeth Conference of 1888] the following Articles supply a basis on which approach may be, by God's blessing, made towards Home Reunion:
(a) The Holy Scriptures of the Old and New Testaments as "containing all things necessary to salvation," and as being the rule and ultimate standard of faith.
(b) The Apostles' Creed, as the Baptismal Symbol; and the Nicene Creed, as the sufficient statement of the Christian faith.
(c) The two Sacraments ordained by Christ Himself -- Baptism and the Supper of the Lord -- ministered with unfailing use of Christ's words of Institution, and of the elements ordained by Him.
(d) The Historic Episcopate, locally adapted in the methods of its administration to the varying needs of the nations and peoples called of God into the Unity of His Church.
Your points (1) (2) (3) and (5) are covered by (b), and point (4) is covered by (a).
To your list I would add:
6. The seven-day week, beginning on the Lord's Day and ending on the Sabbath.
My observations on your points (1) through (5):
1. Here is the Collect for Trinity Sunday from the Episcopal Church's Book of Common Prayer:
Almighty and everlasting God, who hast given unto us thy servants grace, by the confession of a true faith, to acknowledge the glory of the eternal Trinity, and in the power of the Divine Majesty to worship the Unity: We beseech thee that thou wouldest keep us steadfast in this faith and worship, and bring us at last to see thee in thy one and eternal glory, O Father; who with the Son and the Holy Spirit livest and reignest, one God, for ever and ever.
Further comment (my private opinion only): As I read the history, the twin doctrines of the Trinity and the Incarnation were the best way found in antiquity to preserve the truths of the scriptural and Jewish inheritance and of the original Jewish Christian experience in the face of the questions posed by the Gentile world's presuppositions.
2. Here is one of the Collects for Christmas Day from TEC's BCP:
Almighty God, who hast given us thy only-begotten Son to take our nature upon him and as at this time to be born of a pure virgin: Grant that we, being regenerate and made thy children by adoption and grace, may daily be renewed by thy Holy Spirit; through the same our Lord Jesus Christ, who liveth and reigneth with thee and the same Spirit ever, one God, world without end.
Further comment (my private opinion only): It is necessary to distinguish the doctrine of virgin conception, which is scriptural, from the doctrine of "virgin birth", which holds that our Lord's worthy mother gave birth to him without pain or loss of blood. This latter formulation I reject. To me it seems almost to deny the Incarnation. But even if that be not the case, it seems an unreasonable proposition.
3. and 5. Point (3) is clearly asserted in the Nicene Creed (point 5) which the rubrics of our Eucharistic synaxis require to be recited on Sundays and major feasts.
4. Christological interpretations of Isaiah 52:13-53:12 and Psalm 22 are implied by the appointment of these readings among the options for the readings on Good Friday.
Further comment (private opinion only): There is no contradiction between interpreting the Hebrew Scriptures Christologically and asserting that, as a historical matter, the original authors could have had little or no knowledge of the details of how their visions would be understood by future generations to have been fulfilled.
Remarks on other replies to this thread:
A. The filioque
. A detailed Anglican-Orthodox dialog on the questions raised by the filioque
can be found in the Cyprus Agreed Statement:http://www.anglicancommunion.org/ministry/ecumenical/dialogues/orthodox/docs/pdf/The%20Church%20of%20the%20Triune%20God.pdf
Further comment (private opinion only). The doctrine of the filioque
was asserted against the Arians. I suppose the thinking was something like, "If the Father and Son don't share all things in common, the Son does not truly know his Father as the Arians teach. But this cannot be so. So the Father and the Son must share all things." The doctrine is orthodox in intention, though the addition to the Creed long ago outlived any usefulness it had. So the latter is slowly being phased out in Anglicanism, while the former is taught in an orthodox sense.
Any doctrine of the Holy Spirit's procession must incorporate these scriptural facts:
i. The Son "who is in the bosom of the Father, has made [God] known". So the Son must truly know his Father.
ii. The Holy Spirit is called in Scripture "the Spirit of Jesus" (Acts 16.7), "the spirit of Christ" (Romans 8.9), and "the Sprit of [God's] Son".
B. The 2nd Psalm. The translation of Psalm 2.10-12 in my "Protestant Bible" (RSV) is
10.Now therefore, O kings, be wise;*
be warned, O rulers of the earth.
11. Serve the LORD with fear,*
with trembling  kiss his feet,
lest he be angry, and you perish in the way;*
for his wrath is quickly kindled.
Blessed are all who take refuge in him.
In my Book of Common Prayer
(1979 edition) Psalm 2.10-13 is
10. And now, you kings, be wise; *
be warned, you rulers of the earth.
11. Submit to the LORD with fear,*
and with trembling bow before him;
12. Lest he be angry and you perish;*
for his wrath is quickly kindled.
13. Happy are they all*
who take refuge in him.