If it works after you hit it then i would say it probably is a fault with the buttons.
Don't know if they can be replaced or if it means the full steering wheel replacement.
As for the air bag, if you need to go that far then disconnect the battery and leave alone for at least ten minutes. It should then be safe to remove it. I did a similar job on my last car ( replaced the clock spring ) and all went ok. Remember to store the airbag with the side that has the ford badge facing up, then if it does accidentally deploy, it rarely happens, it will stay on the ground and not get launched.
1 litre Zetec Turbo petrol 74Kw / 100 Ps. as in my avatar.