Spoilers for first campaign mission.

In first campaign mission using the app after tutorial.

After rescuing the hostages, IG-88, Agent Blaise, a probe droid, 2 Imperial Officers, a squad of storm troopers and a squad of snow troopers all spawned at once.

Is this the "normal" difficulty?

Hard to say. Probably.

Note that if you continue the campaign after the tutorial, you are skipping the "actual" first mission of the campaign. Start a new campaign without tutorial if you want to play that.

(Also, there's a specific Legends of the Alliance subforum.)

For that section I've had worse on normal, but I've also had a lot better. The game probably thought you were doing too well, meaning you had high fame. If you'd been dealing some high threat groups leading into the event then it's possible.