Is there a warning when the Steam keys of a product are getting low? like I uploaded 200, and there are only 20-15 left (in practice to make sure people don't remain without them)? Or I need to check it manually? If there isn't such a system in place I think would be a good idea (maybe just display a warning/message in the control panel itself).

We currently don't have a notification if you run out. I agree an automated notification would be a good idea! I'll make a note.