Product customization plugin

[Kuubs]

I've got a trouble regarding a functionality I need to implement in Virtuemart.

1. I have a product with 1000 sizes. I want to let the visitor choose the size in different steps. So first he chooses 1-99, 100-199, etc. And after that the user can pick 1-9, 10-19 etc.

2. Next I have a custom field that is the "Product code" field. This field gets filled automatically based on the custom fields they choose before, so size, weight, type, etc.

I think it's possible with just a plugin, especially for the second one, the first one I don't know, maybe a custom custom field?