Which style did you pick? Smart or Loud? I picked Smart, and then I had to do a couple of minor prep missions (the below isn't a spoiler if you've gotten through the briefing and picked the Smart style):
Loud.
But I can't find *any* missions. Not the heist, not any prep missions. The briefing did mention I had to get some guns from an armoured van - is that all it is? I have to search the city for an armoured van and steal guns from it? Or am I supposed to trigger that in some way?