The Church did not write the New Testament to justify her teachings but rather wrote the New Testament in order to record the teaching of Christ and His apostles in direct literal form. The rules for inclusion of a book in the canon were: (1) certainty of apostolic origin; (2) consistency with the core teaching of the Church as she already knew it from the Sacred Tradition and (3) continual use of the book in liturgy. Naturally, the teaching of the Church was broader even in the early times and of course, as the scripture informs us, the Church never stopped receiving the instruction of the Holy Ghost even after the canon was closed (John 14:16, 26).
None of the things you cite are in contradiction with the scripture; some of them simply are not discussed in the scripture much. In that category are the details of the live of Mary and details of everyday piety such as holy water (which reminds us of the baptismal water which is very much in the scripture). Others are indeed taught in the scripture: the equal authority of the tradition (2 Thess. 2:14), and the infallibility of the Church (Matthew 16:18, 18:18, Ephesians 5:27). Finally, the Church never claimed to have written the Old Testament. The Church did, however, take seriously the teaching of St. Paul to Timothy where he said that "all" of the scripture St. Timothy knew froom his youth is inspired by God, unlike the Protestant charlatans that dropped the books of the Old Testament they did not like, to their eternal shame.
Others are indeed taught in the scripture: the equal authority of the tradition (2 Thess. 2:14)
Now you are insulting your audience. In the passage you cited the word παράδοσίς means "precepts", specifically the Jewish traditionary law. The word itself is pretty much fixed in its definition at Paul's time.
1 Cor 11:2-3 Now I praise you, brethren, that you remember me in all things and keep the traditions just as I delivered them to you.
You are going to have a Devil of a time (quite literally) to give evidence that the variety of pagan rituals Rome indulges in, commonly profaned by calling "Holy Traditions", were taught and practiced by Paul himself.
Indeed, it is good that you drew our attention to 2 Thessalonians, because in the heart of the next chapter we read what every good Protestant has done:
2 Thess 3:6 But we command you, brethren, in the name of our Lord Jesus Christ, that you withdraw from every brother who walks disorderly and not according to the tradition which he received from us.
That is, we have withdrawn, as if by command from the Apostles themselves, from the apostate Rome which clearly does not walk according to the "traditions" received by the Apostles. Rome has made up all kinds of laws and regulations just as the Jews did to supplement the Law handed down to them from Mt Sinai. Our LORD had some choice statements regarding the sin the Jews committed and that Rome perfected.
Here is the scene. The scribes and Pharisees who were in Jerusalem came up to Jesus and demanded an explanation from him by saying "Why do Your disciples transgress the tradition of the elders?". We read in Matthew 15 the SmackDown™ delivered by our LORD on these wicked men. "Why do you also transgress the commandment of God because of your tradition?". He then provides an example, then quotes Isaiah 29:13. He then gives us a saying repeated today about the "blind leading the blind into a pit". Clearly, our LORD didn't respect "traditions", characterizing them as "vain in their worship, teaching as doctrines the commandments of men."
What Rome is doing in the form of "Holy Traditions" is perpetuating the prophecy of Isaiah, or as our LORD summarizes "These are the things that defile a man". Rome takes the word "traditions" and then sins in the same manner as the Pharisees of Matthew 15. Rome does NOT honor the teaching of the Apostles, rather the Holy Traditions are a deliberate hijacking of the meaning of the word, transforming it into sin.
Utterly shamefull trying to support something that is clearly condemned in Scripture and even a theme focused on and vehemently condemned by our LORD in the Gospels.