Word of advice: never, EVER give your companion a melee weapon. They go all, "I'M F***ING SUPERMAN" and sprint into hordes of zombies. I just gave Hank a good ol' RPG. He has a bunch of RPG rounds that he's apparently been hiding from me, and he doesn't get himself killed on purpose. Everyone wins!
Single player missions that gave a certain amount of money the harder the level is, say the easer levels give 50 coins and 50 xp, and so on would be nice.