Set Quantities of Sale Woocommerce

I hope someone can advise if there is a way to accomplish what i require, either by plugin or work around.

I am developing a site which sells 10 different hand made greetings cards.

The cards are not available for single unit sale.

The cards are only available for sale in packs of 5, 10 or 15.

What i would like is for each card to be available as a single product with and Add to Cart button but without a Single Unit Price, allowing the customer to add individual Cards to Cart.

However i then wish for a limitation to be set where the customer can only complete checkout if 5, 10 or 15 cards are added to the cart.

I would like it to be possible for the customer to add 1 of each card or 5 of 3 different cards or whatever quantities of each card they like, allowing them to make up a set pack with which ever variations they choose.

I trust this sounds a little complicated and would greatly appreciate any direction you may have on the best way to accomplish this.

Thanks for your help.

http://wordpress.org/plugins/woocommerce/