Savannah here from the Shopify Guru Team.
When it comes to listing your products, are you hoping to still list them by the product price, rather than the case price (but only allow the purchase of cases)? If so, I'd recommend checking out an app like OrderLogic or MinMaxify to limit order quantities.
If you plan on listing the price for each case instead of each product, you may just be after an app to sync the inventory of each individual item. You can use something like Product Kits or Product Bundles. If you're listing prices based on the case, you can set your product variants up to read Quantity: 1 Case and attribute a price to each amount.
Let me know if there's anything I can clarify. Our Guru Team is also here to help 24/7 with live support: https://help.shopify.com/questions.