Since Rey asks about the validity of the rumoured spy, I prefer the original version of Boolio confirming that “There’s a spy in the First Order”. And since said spy is Hux, he would probably point out that it was The supreme leader himself that found the fleet, not The First Order. After all it was entirely his initiative and would emphasis that he’s been searching for said fleet for a while.
It’s why I would do the first part like this:
Finn- “got something for us?”
Boolio- "There’s a spy in the First Order. The Supreme leader, he’s found something, the rumoured hidden fleet from the old war.
I really like the rest of the dialogue you’ve written.