This is technically possible to achieve currently but the exact implementation would depend on your business processes.
Are you holding and fulfilling stock from physical locations or are you shipping orders to the physical sites from a single distribution point?
If it’s the former we would currently advise a multi-store setup and sync product data across them, with stock levels managed for each physical store inside each individual store.
If it’s the latter this can be achieved with a single moltin store and use flows (custom schemas) to create your 600 physical locations for pre-defined shipping addresses that your customers can then select from (or based on the closest physical location to the customers location if you have that data to hand).
In either scenario you could create a custom order status attribute for when the physical location receives or has in stock the order items. From this you could integrate moltin with Twilio to send an SMS or push notification to the customer or a mailing service (Sendgrid?) for email.
We have plans to build on top our inventory service to support this use case within a single store but that is currently lower on our priority list to complete.
Hope this was helpful!