1. For what purpose does Fences, Act 1, Scene 1 begin with Troy and Bono discussing
Brownie, a seemingly irrelevant character?

To give an underlying idea of Troy's personality and his way of thinking through out the story, the author has started off the conversation from a vague perspective of an incident with an unknown character to the reader, Brownie.

Explanation:

August Wilson's writings are realistic and practical. In his approach towards portraying the character of Troy in the drama Fences, he starts the drama with a conversation that involves an incident from the past. The character of Brownie, though unknown to the reader, the author convinces the reader to understand what Troy is, as a person, when he talks and ridicules Brownie's behavior. It makes the reader understand that Brownie's character is opposite to that of Troy's.

what are your options ?

i would say years or cherry blossoms