The Gemarah does not seem to make much mention of the 54 Torah Parshiot in the annual Torah reading. I don't know, offhand, what Ramba"m mentions about them either.
- Who organized both the annual and tri-annual readings, in general, and when were they organized? Why were there differences (annual vs. tri-annual)?
- How were the Parshiot decided? (Where each Parsha begins, the Parsha "names", Breishit, Noach, etc. (I know the name is taken from a word near the start of the parsha; I'm curious who decided on where each Parsha begins?)
- Who decided which Parshiot should be doubled?