Need low-stock reorder alerts with recommended order quantities

We run an online store with several hundred SKUs, and right now stock levels are tracked manually. That means we regularly find out a product is out of stock only after a customer has already tried to order it, and the order gets cancelled or delayed while we scramble to restock. We need someone to build a threshold-based alerting system: for every product in the catalog we want to set an individual minimum stock level, and as soon as the available quantity drops to or below that number, the purchasing manager should get a notification right away instead of finding out days later.

The notification should not just say that an item is running low. It needs to include a recommended reorder volume calculated from that product's recent sales history, so the buyer does not have to open a separate report and guess a number by eye. Ideally the recommendation should react to actual sales speed rather than a fixed formula, so a slow-moving item does not get the same reorder size as a fast seller, and seasonal spikes push the recommended volume up rather than leaving it stuck at an average.

This is purely a purchasing alert layer, not a two-way inventory sync with any outside system. We already keep our own stock records; what we need is the logic that watches thresholds, computes a sensible order quantity, and delivers the alert. Delivery can be by email or inside our internal admin panel, whichever is more reliable to build and maintain.

What the finished solution should include:
— a configurable minimum threshold set separately for each product
— an automatic check that fires as soon as stock crosses the threshold
— a recommended reorder quantity calculated from sales history
— delivery of the notification to the responsible purchaser
— a simple settings screen for adjusting thresholds without needing a developer