A friend of the family has asked me to assist her in making her own wedding cake... no problem except I only have a bit of practice with fondant. The problem is the cakes are 16", 12", 8" (6 inches high each).
I need help figuring out how to roll out that much fondant without it sticking and then picking it up without it tearing... I am sooo stressed

Invest in piece of clear vinyl sheet - the kind you sometimes buy as protection for tablecloth (if some people do it in US too as well as grandmas here). Roll the fondant on this sheet slightly larger than you need for covering the cake. Take the fondant *with* the sheet to your cake, flip it over, position where you need it and peel the vinyl from the fondant. If you are careful, you can even reposition it a bit as long as it is still supported with the vinyl. The see-through vinyl is nice - you see what you are doing.
One problem is the size of fondant you would need to cover the largest layers - for the 16" it would be 16+6+6 inch - you need a circle of 29 inch minimum, better of 30 inch. Best would it be if you can get your friend to help you - one of the few occasions in cake decorating where two more hands working on the same cake help.

Ideally, try to find a design, where little flaws can be covered - either with flowers (real or fondant) or with another accents (fondant or whatever...). You can make it white on white or in wedding colors.

One of the most difficult wedding cake designs is the "simple white, only with one layer covered cake".

Good luck to you and your friend.