Ok here you go...Mind you these are images from my file and I'm still trying to get in your head. So tell me what you love and hate and we'll play with it. After looking at these images I think gray would make a great base color because it makes the orange and pink pop and it's lends itself to being more vintage that brown, black and ivory.
I love your save the dates and the idea of the message in the bottle. How are you sending them? Did you create the inside portion yet? Maybe using a retro/vintage font and style would mix nicely with the beach. Pearlized shells will aso give you a glam look. Have you seen what futuremrstgun did with her starfish? She used Martha Stewart Glitter paint. That's a great way to add bling to the beach for your invitation and decor!
I love the site idea. Not sure what your able to bring or get from there, but I would replace the tiki torches, maybe with chandeliers or lanterns.
The way I do Interior Design when I'm doing a contrast of two different styles is a balance of the two in each item or two things together with one of each item. It's difficult to explain with words, but I'll try because it's what I envision would work perfect for you. This is my favorite way to design, it's what I'm doing for my own wedding.
What's contemporary right now is to take something old and give it a splash of a bright color to reinvent it. You'll see modern classic furniture, chandeliers and baroque furnishings being painted bright, fun colors like aqua, pink and chartreuse. I did this in a design for a restaurant. I used a tradititional style table with balustrade or turned legs but made it clear acrylic. For the seating I used traditional french provincial frames but the frames were painted aqua and chartreuse and the fabrics were classic patterns in bright colors. You could do this by choosing a vintage style shoe - but in hot pink. You can use the vintage flourishes and scroll frames and script font but put them in bright pink and orange.
The other way to do this, and you can use a combination of the two is by mixing closely related items with one of each style. When I did an apartment that was the juxtaposition of Industrial and Traditional it was using a lot of what the client had so I approached it different and it worked. I've seen a some furniture catalogs lately that use this method also so it should look familiar. They had old colonial eyebrow chairs in the dining room that were in great condition. We added a durable fabric and placed them in the kitchen paired with a simple steel table on locking wheels. You can do this by having a vintage, glam dress with beachy accessories or vice versa for you and your girls.
There has to be a balance for it to all come together but as long as I have the free time I would love to help you.