This one is fairly straightforward. But, because the game can be/is glitchy, I thought I'd put down what I did.
First off, save, save and save. Every 1 or 2 items I did a Quick Save to be safe.
I did the Burn Baby Burn and Med Tech cheevos to start. Again, to avoid any nasty surprises down the road. I've had enough of them with this game. These items are all clearly marked on the map. There's a guide for Burn Baby Burn. (I did most of those with a Roller Hawg and used the Flaming Arrows for the ones I could not get to.)
I then did Episode 1.
Shortly after completing those, I got 4 Side Missions for the ZDC cameras. One for each of the 4 areas. There are 7 cameras in each area, except for S. Almuda, which has 8. They are clearly marked on the map when you highlight the area you are in on your Side Missions list. There are none on any of the bridges.
According to spanky:
To anyone needed help with restarting...
I found that you ONLY trigger the side mission if you travel to S Almuda via the southern bridge (near where you have a "protect" main mission). Taking the northern bridge won't do it.
Posted by spankyNspronkle on 19 Jun at 23:06
I started in S. Almuda and worked my way counter clockwise. The zombie count seems to be higher, and, there are a few more barriers. So, I either made a vehicle or picked up whatever I ran across. Jumping on the roof of your vehicle to take a shot is advised. Otherwise, the Zombies mess up the shot and/or inflict heavy damage.
There's a new barrier going from S. Almuda to Central City via S. Bridge. Not to worry, there are a van and street cleaner right on the other side of the barrier to make a Party Slapper. Launching Zombies as fireworks is worth the price of admission for me!
Happy hunting
Edit: UnsungGhost commented that the one near the power plant in S. Almuda was destroyed, but, still blaring away. (glitched - the game has a lot) So, it would be a good idea to do these as soon as you open an area and get them all before moving on.