good ideas man, but I dont think that reduceing the speed of zombies would be good, only becuase the game is about surviving a zombie apocalypse and if they are to slow it would be easier to get away, therefore zombies would slowley not become a threat (just my opinion). But if you slow them down and give them more damage it might work, or you could even speed them up and make them do less damage or just have three different types of zombies, fast ones that do low damage, mediumly fast ones with medium damage and slow ones with big damage. (just my opinion). apart from that, they are good ideas :)