Although we don't have email or popup notifications, you can create in the Inventory dashboard a Bookmark card of 'On-Hand Inventory and Alerts' type with the 'Show only products which need to be ordered' checked:
You can do this for specific locations and/or for specific suppliers and that way you can create multiple such Bookmark Cards.
That way the cards will show non-0 quantity whenever your On-Hand availability is below the Alert Level you have set.
So, our suggested approach is for you to regularly check the Inventory dashboard for these non-0 quantities in these cards and make purchases as necessary. The regular checks can be once per week or once per day (depending on the volume of your transactions) or simply after a sale has been fulfilled and stock may have fallen below the alert level.