Actually, I know the solution that will be definitely useful in your situation. It is called Automated Product Import. You can benefit from it, since if I understood you correctly you need constantly update your store with the file from supplier automatically and on schedule each period you need. This application is desktop and can be used in combination with Store Manager for Magento software only.
Using the combination of those 2 products all you need to do is to set up import for the first time and set the time of scheduled update and all the further updates will be done automatically taking the data from your supplier.
I will go through the specific questions you asked and give explanations concerning that applications I offered.
Magento uses category ID\\\\\\\âs. With the CSV from the manufacturer we get a lay-out like this: Main article group -> Sub article group -> Subsub article group. Also they used \\\\\\\"product hierarchy\\\\\\\âs\\\\\\\â
I examined your file and saw that you have categories and subcategories in separate columns. For Store Manager and Automated product import categories and sub-categories (category path) should be placed in one column. However, it is not the problem, since the columns can be easily merged. So Store Manager can handle import of the data like that.
- When you want to sell products with different sizes in 1 product, you have to use the grouped products option. In this CSV the products are ordered separated.
- Product relations are made in the columns Product Relation1, Product Relation2, Product Relation 3.
Also I noticed that in the example you provided, product relations are empty. Can you provide the example of the values you have indicated there?
Since generally, if you have SKUs of related products there (those related to grouped product), then they will be imported correctly with correct relations and from frontend will be available as separate products as well as in groped product page (as variant to choose).
In any case, here you can find 14-days trial versions for both Store Manager and Automated Product Import - http://www.magentocommerce.com/magento-connect/store-manager-for-magento.html
If you have any questions, please ask and I will gladly help you if any assistance required.