How much bandwidth does the downloader consume?
That's a good question, and the short answer is that the bandwidth consumption should be insignificant - approximately 0.25 Mbps for 1 min for every 100 photos downloaded.
To put that in perspective, you would need to be downloading more than 100,000 photos per hour to consume the same bandwidth as one person streaming Netflix.
The longer answer is that it depends on the resolution and the total number of photos you're processing at a specific time (and a host of other factors). The average file size for a downloaded photo is 10-20 kB. I'm not sure how many photos you expect to process during your peak times, but if you estimate that at peak times you might process 100 photos per in a 10-minute window (that's 1 photo every 6 seconds), the total download size for 1 run of the downloader would be ~1.5 MB. A 100 Mbps connection, which would be very modest for any enterprise network, could theoretically download that in less than 1/7 of a second. More realistically, due to back and forth "conversation" between the API and the downloader and any throughput limitations of the many public and private servers between the API and the downloader, the bandwidth consumption for each 10-minute interval would probably be more like 0.25 Mbps for 1 min followed by no traffic at all for nine minutes.