What is the origin of the structure of the Aliyot and the Torah reading, the B’rachot, when to stand?
Moshe Rabenu is the first to establish the Torah reading with a Minyan on Shabbat Mondays and Thursdays, Ezra added Shabbat Mincha reading, between the two, the number of Aliyot was also decided. Moshe also established the readings for the Chagim. From the Zohar it appears that the weekly Parashot were divided and designated by Moshe as well. (Mishnah Brurah 135, Piskei Tshuvot ibid 1) The dividing of the Aliyot within the Parasha isn’t from an authorised source and has no holy meaning to it (ibid 138 2) The Brachot were introduced by the our sages and are learnt from a Pasuk (Brachot 21a) Standing during the torah reading is depended on your custom; it seams like most people sit. (Shulchan Aruch OC 146 4)