Why don't you read "The Faith of the Early Fathers" by William Jurgens? You will find out what the traditions were and how the early church worshipped in the first 300 years. There is quite a lot of writing from that time period. Off hand I would suggest the writings of Ignatius, who was martyred in Rome +/- 100 AD and Justin Martyr, who was martyred +/- 150 AD. You can read what they say about the Early Church. Their writings are included in the "Faith of the Early Fathers" book.
In Thess, Paul tells them to:
2 Thessalonians 2:5 Therefore, brethren, stand fast, and hold the traditions which ye have been taught, whether by word, or our epistle.
Notice that the underlined section is action that was completed in the Past.
These are traditions that existed PRIOR to Paul's death, so certainly they were not tradition brought about by people who lived AFTER his life was over.
What are they? Where are they listed?