You unlock the cheat menu and cheats as you finish the best ending for each guy's route. Each Guy unlocks a unique cheat. So you have to play the game all the way through before you start getting cheats.
That isn't correct at all. I was able to easily win the Seiyuu Award in my first playthrough, going after Shiba. Got his best ending and won the award. So no, you are not locked out of best endings with other characters by not going for Toshiyuki first. =T
