You can have the same ball position for all clubs. It's the stance that is wider or narrower so it appears that the ball is farther back or forward as a result. Or, you can have the ball at different positions according to the club you are using or according to the shot you are playing.

For example, you could put the ball back for a punch or for a low shot under a tree. Or you could put the ball forward for a flop shot or to adjust to the slope, etc.

You could swing the same way for all club. Or not. You could swing steeper for short clubs and flatter for longer clubs, etc. Or you could adapt to your clubs' lie angle and swing accordingly. Or when you tee it up.

I read frequently that irons should be hit downward and the driver should be hit either flat or slightly upward.

There is no rule or law that either forces you to swing a certain way or that prevents you from swinging a certain way. After all, you choose what you will do with the club in your hands.