Alright, I'm late with my opinion.
1. I really liked the idea of the placecard holder, but I have to agree that Tammy(host) made some very valid points, so maybe doing the cakes and holders seperate would be better.
2. I did a beach theme wedding shower for my sister last year and my aunt made the cake because that's what she does, I wanted a sandcastle cake, but too hard, so she did a 3 layer cake, it had beige frosting and she had graham cracker crumbs all over it and she did the seashell chocolates for it, but she did a lot of them in a marble color, so they weren't just white or just dark, that might be a better option. If I could get the damn picture to post I'd show you guys, it came out really nice.
3. I know you said you didn't like the buttercream, were there any others you liked that were lighter in color?
4. I heard fondant is really yucky, but I've never had it.
I hope some of this helps!