How many people are called up on Shabbat: Megillah 21a, 23a
How many people are called up on Shabbat afternoon: Megillah 21a, 21b, 24a
Adding people called up to the Torah on Shabbat: Megillah 21a
Adding people called up to the Torah on Shabbat Afternoon: Megillah 21a, 23a
