Magneto custom module

I have a Magento modification that I need completing. The problem: On a new Magento website we are creating, the customer is only allowed to purchase 1 of each particular product SKU, due to it being a samples offering. At present we have set the maximum qty allowed in cart to 1 and this works as required for simple products. In offering pre-built sample packs with a selection of preselected products, as far as I see it the best way to do it is to use bundled products. However, when a bundle product is added to the cart alongside a simple product that is also part of the bundle, Magento doesn't register the clash of SKU and allows multiples of each product in the cart (i.e. one from the single product and one from each bundle the product is in). Requirement: To recognise a clash of SKU between a simple product and product within a bundle (or within 2 bundles) and not allow them to be added to the cart together, and tell the customer why. Desirable: If a clash is noticed, the bundle product is still added to the cart but any identical SKU's are removed from other bundles / simple products and the customer is notified with a friendly message e.g. "Some products within this sample pack are the same as products you already have in your cart and will not be added to your order." Prices of the bundles obviously need to be adjusted accordingly. Note: In many ways this may be easier to achieve with a Grouped product instead as products from a group are added separately. But there is a similar problem with adding a simple product to the cart that has already been added from a group. Plus we would prefer to keep our sample packs as sample packs in the cart (i.e. bundles). Magento: The software needs to be written as a module so should not overwrite any core files. Ownership: The module and rights to its use or sale after completion of the project are negotiable