Did Saul and Max ever meet before
I guess, realistically they wouldn't have done. Saul was the director of the CIA and Max is a technician who was working for one of his agents (Carrie). There would be no need for Saul to have met or dealt with someone several rungs of the ladder below him (no offence to Chandler lookalike).
Do we think assassin set up the whole thing, bumping into astrid to make Quinn suspicious then sending a stooge to the motel?
No, I think the guy at the motel thing was just to show that Quinn's judgement isn't always great. It was just a plot vehicle to get him to question his own judgement and go and apologize to Astrid. I think he genuinely did see the real assassin guy in the shop, but then just made a mistake and picked the wrong guy at the motel.
And I doubt that Dar ordered Astrid to be killed, I'm guessing he just brought her in to babysit Quinn and keep him out of the way, then sent the assassin in, who got a bit gun happy.