“It’s the First Order” sounds great. “They’ve done it.” is okay in that scene, just like RogueLeader said, but I’m not sure if your first idea with the Finn running shot split in half isn’t the better solution. Both versions work quite good I think.

The thing I don’t like about your mock-up is the placement of your scene. As I explained earlier, I’d keep these shots where they were in the original movie before BB-8 reaches Rey. There are two reasons for that:
First of all, it’d give Finn and Han more time to get to Maz and in the cellar for the lightsaber. But more importantly, it would allow the TIEs/Stardestroyer to be seen from a bigger distance, thus giving the people a reason to watch for what’s coming instead of running away like they would if TIEs were right above them.

Also, as a sidenote: Where did you take the “It’s the…” from for the First Order line?