Hi,
1. Yes it is possible, you can create custom product fields and then set the values on the product edition pages, or via the mass actions to be fastest.
2. The best is to take example on the plugin "system / custom_quantity_width_length_weight"
3. If you set the custom fields to not be displayed on frontend so it is safe. As it require PHP code to display their values, so end customer can't see it.
4. No problem for the end formula, it can be used in the plugin directly.
5. We don't do this kind of customizations, but you can post a request in the commercial jobs section of this forum.