I am doing a 3 tier square wedding cake in April. I made the bride a sample of a cake covered in mmf and buttercream smoothed out with the viva method. The bride had indicated that she hated the taste of fondant.
( I found this funny as she had tasted a lot of samples at a local bridal show) I would think vendors would use a great fondant such as Satin Ice when handing out samples. Her and her husband to be fell in love with the mmf, she said it was outstanding. Better than anything she tasted at the bridal show

Anyway, do you just follow the chart like in the Wilton yearbook for quanities needed or does mmf yield less or more than the packaged fondant.

You'd use about the same amount weither you make the fondant, buy it or use mmf. The only differences would be how thick you roll your fondant out.