This game has a feature to make it enjoyable for interaction along with Twitch viewers. In the twitch chat you can input commands that can aid you on your way to level 30. You must have a Twitch account. You don't need to be broadcasting but you do need to link your Twitch name with the game at the main menu under options. There is a cool down to most of these commands. All achievements are very obtainable using this feature. But you're going to have to grind out the 500,000 kills.
http://kilallzombies.wikia.com/wiki/Streaming_interactionskillallzombies ( kills all the zombies on the board)
redpill (revive player)
There are input commands for every type of gun so you can easily get the 1000 kills with each of them.