PHP Shopping Cart Modifications

I have a custom php mysql shopping cart which needs an upgrade. At present you can add items to the cart apply discounts calculate shipping etc. I want to extend functionality I need itemised costs for the following. 1. The ability to add custom product attributes in the admin area.( size, colour etc with price variation if necessary) Then the ability to selectively apply these attributes to the products. 2. THe option on checkout for the shopper have their details "remembered" they get the option to choose a password, they then get emailed a username and password. They can then login and view their order history or change their details. Thanks