I will be making my first rice paper feather wedding cake and don't know where to start, I also want to know how long it will take before it droops.

Can you give more information?  If you are putting the wafer paper feathers on fondant, I don't see a drooping problem.  Don't know about butter cream cause the paper is going to react to any moisture.

http://www.kitchenkrafts.com/product/rice-paper-8-inch-x-11-100-pk/cake-airbrush-tools-and-supplies

plus on amazon there's better prices

I will be using rice paper on fondant.

If this is the look you are going for, scroll down into the comments and she tells you how she did it.  I have attached feathers to fondant with royal icing also.  It doesn't take much to have them stick.

http://cakecentral.com/g/i/1530029/my-attempt-at-a-feather-cake-feathers-are-1-strips-of-rice-paper-and-dusted-with-rose-luster-dust-glass-beads-were-added-to-give-it-some-sparkle/