You can use BAM. This will allow you to report on what is happening from the aggregated data – this will not be much use as a validity check in the Orders system and will probably duplicate reports from the Order system.
You can total values in a map. You can use the RecordCount functoid to count the number of orders per file and the CumulativeSum functoid for the total orders value. To sum product quantities or amounts will probably require some custom Xslt in a map as you will need to group products by SKU .