My good friend asked me to make a cake for their wedding reception (already got married on beach in bahamas) SO im gonna do it for them as my gift to them... but i have no clueee how big to make it or what to put as a topper or if i should assemble it there or where i make it.. Its for 80 ppl. IT gonna be a simple round cake with seashells on it with 'sand' underneith the white chocolate shells (probley with one pile of shells on each tier so its kept neat and simple). SO anyone whos made one of these cakes and has any advice for me would be greatly appriciated. Thanks for looking!

I've made one similar to what you are talking about. (DH had me make his friends cake for him as a gift who was married in the Bahamas and a few weeks later had a reception for 150 people) Mine is in my photos.
I made all of my shells one week in advance and figured out a time line that would work for me.
I follow Earlene's servings chart instead of Wiltons, there are slightly less servings with her serving chart.

Are they wanting to keep the top tier for their anniversary? If so, I recommend a 6-9-12. Here's Wilton's link... (I used to use Earlene's but she really uses considerably larger pieces). This will give you 88 servings and they keep the top tier.

http://www.wilton.com/wedding/cakeinfo/cakedata.cfm

no they wont be keeping the top tier, if anything the groom will eat the top tier to himself because he is a cake eating freak!! hahah And ill be cutting the cake, probley to the sizes people will want. Theres usually more ppl who want a small piece then a big piece (i like BIG pieces!! YUM!) Im sure he would LOVE to have leftovers also to bring home and eat for a week! haha so i want to make sure i make more then enough, but not toooo big. I only have one mould for the shells so i guess ill start working on them about 2 weeks in advance. Did u make the ones that are white chocolate and kinds sparkly? or are they more real looking? im planning on doing them white with luster dust... im not surehow to apply lust dust to chocolate though.. also how did u get your shells to stick to the cake? thanks for the sizing chart!!