About the tshuvah/Repentance: As far as any reference w/in the scriptures, I've never found this word, nor any mitzvah to observe this in the form of an annual observation. The original texts show the word [שוב (Heb.), or ושבום (Aram.)], both of which are defined in English as "to turn about, to return" and/or " to turn about, to return".
The Mishneh Torah (Hebrew: מִשְׁנֵה תּוֹרָה, "Repetition of the Torah"), subtitled Sefer Yad HaHazaka (ספר יד החזקה "Book of the Strong Hand"), is a code of Jewish religious law (Halakha) authored by Maimonides (Rabbi Moshe ben Maimon, also known as RaMBaM or "Rambam"), one of history's foremost rabbis. The Mishneh Torah was compiled between 1170 and 1180 (4930–4940), while Maimonides was living in Egypt, and is regarded as Maimonides' magnum opus.
It begs the question whether one is to observe rabbinic Judaism's tradition, or the scriptures? Thoughts?
There is indeed no mitzvah commanding an annual observance of t'shuvah. And you are correct, the root of the word is שוב (Heb.) But there are many scriptures expressing YHWH's expectations of us to return to Him and to stop sinning, and as the annual time of this is the day of Yom Kippur, there is certainly ample evidence that what we know today as "t'shuvah" is in complete compliance with Torah. As to the traditions of t'shuvah, no, we are not obligated to conduct ourselves in accordance with the rabbinic procedures. But since all parts of t'shuvah come from scripture, the tradition is not at all "bad".
In Judaism, for example, many verses in liturgy are "chanted", and there is no mitzvah requiring that either, yet it is a wonderful way to actually remember the scripture or the commandment, liturgy, or ceremony. Everyone, even a non-Hebrew speaking person can remember the words to the "Sh'mah" in Hebrew because all they have to do is chant it! But few can remember the words if they have to just speak the phrase. My husband once presented an excellent teaching on Yom Kippur and t'shuvah at the synagogue we attended, if you're interested.
No commandment for "t'shuvah" is found in scripture but the word is found many times to mean "to turn" (back, to or from), "return", or "repent" - all in the context of turning from sinful ways and returning to YHWH - exactly those aspects of propitiation that is the tradition of t'shuvah. See Psalm 7:12, Psalm 90:3, Hosea 6:1, Isaiah 6:10, Isaiah 10:22, Jeremiah 3:7, for example, and many others.
And the annual aspect of it comes from the observance of Yom Kippur, the 10th of Tishri, the ONLY day the High Priest was permitted to enter the Holy of Holies to make atonement for all of Israel - Exodus 30:10, Leviticus 16:29, Leviticus 16:34.
While we agree with you that the halakha of rabbinic Judaism carries more weight in some circles than it should, we would say that we might want to first make the effort to understand the Torah origins of the halakha before we dismiss it. In other words, spend less time with Rambam and more in the Word....