Regardign Romans 5, you started by saying that St. Paul somehow was contradicted by the teachings of the Church regarding Mary. You now have seen that it is your interpretation of Romans 5 that is contradicted, but not the text itself.
Regarding the authority of the Church, — it is in the Scripture. See for example the authroty to “bind and loose” that Christ gave the Church, and the promise of continuing divine councel in John 14. The idea that unless we find something in the scripture it should not be taught, however, is not itself in the scripture. It is also absurd, because, naturally, lives of saints, including the Virgin Mary, exceed the scope of the Scripture.
The criterion for orthodoxy is not what is and what is not in the scrupture, but rather:
1. Is the teaching compatible with other infallible doctrines?
2. Is the teaching compatible with the Scripture (this is nto really a separate requirement but I list it separately for clarity)
3. Is the teaching of apostolic origin in some form?
On the assumption of Mary, all three are satisfied.
On the fallacies of Luther all three fail. Most notably, the doctrine of “sola fide” is directly contradicted by the scripture, and “sola scriptura” is at best not supported by it, and clearly contradicts the scripture when it is used to deny the authority of the Church.
There are many warning in the scripture about false doctrines of men. They all apply to Mohamedanism and Protestantism amply and prophetically.