A salvo is when military troops are in a battle and they all fire their guns at the same time. In the sentence you posted, "opening salvo" is being used figuratively. It means a verbal attack. The term means that politicians who are on opposite sides are going to both strongly advocate for their position in a verbal "battle."

Okay, let's dive in... "opening salvo" is the first question when many questions will happen "fast-track talks" are talks or conversations that happen fast or were scheduled to happen very soon after the request. They do not have a delay of asking or waiting for other things to happen. "To reel from" something is to feel shock because of something or to react to something