Just a suggestion, if you could make a different way to view and choose your existing Konpanions, that would be great. I have 41 of them, and it was quite bothersome to sort through them all.
To get the zombie badge shoot with the pistol for as long as you can, aiming at the head if possible. You should last a minute before they get to the wall. Then switch to the shotgun and aim at groups right in front of your wall. Bigger groups first. + if it helps!
Little tip to get the 600m/ft badge: Max everything, and on the ramp ignore the "jump in the cart" and on the "take off" max it. I got 700 first try like that. + if its useful!