You should be able to cover all of your dummies with a full recipe, just start with the largest and work your way down. As far as using it the same day, it's not impossible, but it will be sticky. I've had to do it in an emergency and it was managable. It was also very early in my cake "career" so as a more experienced fondant user, now it might not be as challenging as it was then. I would suggest using corn starch to roll it out and sprinkle a little on top of your fondant before you start rolling, too. Also, if you have any time between making and covering, give it a little time in the fridge. That seemed to help when I had to do it. Good luck!!