My strategy for this mission was to take out as many as possible using the tech in the alleyway.
To do this, I'd run and grab a car and beat them to the alleyway. I'd park the car anywhere on the street, it doesn't matter where - you're not using it to block them.
Directly across from the alleyway is another walking area with some concrete gardens etc on the sides, you can hide behind one of these. From there, hack the cameras until you get to the one that's in the middle of the alleyway, you should be able to see the convoy coming.
Once the convoy reaches the alleyway, you should switch to the camera that overlooks the exit. When the lead car nearly reaches the exit, bring up the blockers. The lead car will back up over a transformer (?) in the ground that you can blow up - do this, blowing up the lead car.
Quickly switch to the rear cars and blow the devices near them. They should get out - one of the drivers will be carrying a cellphone you can explode. Do this, and it should take out the rear car and block the knock-down targets in. If you have trouble with this, plant some IEDs beforehand and use those.
From here, you'll have to shoot your way out. I was able to just wait for them to come to me and I could take them down with an assault rifle. The two knock-down targets waited in the alley, and I just had to sneak up close enough using cover to knock them down.