Most suitable database design for multi store inventory?
This is not a challenge for one, modern RDBMS. You will realize you do not want to have one database per store the first time executive management asks for &quot;How many iPhone 7s do we have on hand across all stores ahead of the new Apple launch?&quot;
I have seen retail systems managing several hundred thousand SKUs across several hundred stores. The master inventory was one ~10 million row table with columns like:

Store ID
SKU
Units on hand

If you use partitioning on your table, queries can be sub-second.
Edit:
There is an open retail data model that handles multiple stores that you can see here:
http://www.omg.org/retail-depository/arts-odm-73/