So I make a product with tons of variations.  So lets say I have I have 10 variations - with 20 in inventory for each variation.  I also sell 'boxes' or 'sets'.  So I have "Box of 4" set up as a product and it seems I can go ahead and list 4 of each product. But how do I leave that part empty and choose from the 10 variations at the time I sell the box of four?  So far I think it has to be just a product with each possible combination.

So what is standard process of selling a "box of 4" and at the time of sale - I can select which four the user wants and use that inventory?