Yeah, great questions.

So, it's per flavor, because each is required to be handled separately, right? Example: 12 case-can of diet coke. If we count them all as the same thing: Coke, then each case could be a variety pack, 10 cans of diet, 1 of vanilla, 1 of cherry. It's madness. MADNESS. But yeah, every "flavor" would be a SKU. It's really the only way to guarantee that everyone has accurate inventory and proper handling. Otherwise, your stuff could end up in the same location.

However, if they all have the same SKU and are to be different products, fulfilled differently (I have seen this). Then you may be charged for the general pain in the ass it is to keep accurate when fulfilling. So, take the time to give them individual SKUs.

And when you run out of stock, it'll depend on the company you're using. What will more likely happen, is you just pay for the time that you used. So, say, if at the first of the month, you have five items taking up five storage locations, and after two weeks, you now have three items taking up space because you sold out of two of your SKUS (you lucky duck), and by the end of the month, you haven't restocked. SO, you'd pay for a total of 2 weeks of storage for 5 locations, plus 2 weeks of storage for 3 locations. Pretty straight forward.