In discussing the two great lights you refer to Yoma 62b where the gemara comments that plural implies at least two so the fact the Torah states two goats means we have to learn something special about them, namely that they must be identical. Why does it not just mean they are just two goats and lights, notthree or more? Why look for more complex reasons?
There is a concept in the Gemara called "Tafasta Merubah Lo Tafasta; Tafasta Muat Tafasta" -- "(If) you take the large you have not taken; if you take the smaller you have taken." This concept tells us that whenever we would be unclear about an amount in the Torah, we should always assume that the Torah refers to the smallest amount. The Gemara uses this principle often as a guideline when investigating the Torah's true intent (i.e. see Sukah 5a).
Take Care,
Yaakov Montrose