"I think they did precisely what the Messiah taught them to do."
This means they said the Our Father because the Messiah taught them to do so.
"Giving up Sola Scriptura, going by tradition or speculation, one can reason that they also recited the Shema prayer for example, and not just the first verse of which the Messiah quoted in the Gospels as the Greatest/First commandment."
This means if we turn from scriptural evidence and to our own speculation, I speculate they also said traditional Jewish prayers that the Messiah would have approved of, in this case, portions of scripture. They may also have said the Kaddish, if it was in use at that time. They may also have said the Priestly Blessing if
The Priestly blessing has been used by the Catholic Church since the first centuries.
We know they asked the Messiah to teach them to pray and that He taught them the Our Father. None of this indicates they
only said the Our Father.
Returning to the scriptures, there are other prayers some or all of them prayed specifically, and there are references to observing the Jewish hours of prayer (Third Hour/9am, Sixth Hour/Noon, Ninth Hour/3pm) and other liturgical prayers.
And they prayed, and said, Thou, Lord, which knowest the hearts of all men, shew whether of these two thou hast chosen, That he may take part of this ministry and apostleship, from which Judas by transgression fell, that he might go to his own place.
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Now Peter and John went up together into the temple at the hour of prayer, being the ninth hour
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And when they heard that, they lifted up their voice to God with one accord, and said, Lord, thou art God, which hast made heaven, and earth, and the sea, and all that in them is: Who by the mouth of thy servant David hast said, Why did the heathen rage, and the people imagine vain things? The kings of the earth stood up, and the rulers were gathered together against the Lord, and against his Christ. For of a truth against thy holy child Jesus, whom thou hast anointed, both Herod, and Pontius Pilate, with the Gentiles, and the people of Israel, were gathered together, For to do whatsoever thy hand and thy counsel determined before to be done. And now, Lord, behold their threatenings: and grant unto thy servants, that with all boldness they may speak thy word, By stretching forth thine hand to heal; and that signs and wonders may be done by the name of thy holy child Jesus.
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On the morrow, as they went on their journey, and drew nigh unto the city, Peter went up upon the housetop to pray about the sixth hour:
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And on the sabbath we went out of the city by a river side, where prayer was wont to be made; and we sat down, and spake unto the women which resorted thither.
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And it came to pass, that, when I was come again to Jerusalem, even while I prayed in the temple, I was in a trance;
Acts, Catholic chapter one, Protestant verses twenty four to twenty five,
Acts, Catholic chapter three, Protestant verse one,
Acts, Catholic chapter four, Protestant verses twenty four to thirty,
Acts, Catholic chapter ten, Protestant verse nine,
Acts, Catholic chapter sixteen, Protestant verses thirteen,
Acts, Catholic chapter twenty two, Protestant verses seventeen,
as authorized, but not authored, by King James We know they asked the Messiah to teach them to pray and that He taught them the Our Father. None of this indicates they only said the Our Father. I'm glad you made that clear. I was beginning to wonder with the rote form of worship in Roman Catholicism if ya'll only said the Lord's Prayer/Our Father, Hail Mary and Rosary and would believe the disciples only said one or two prayers.