I'm not sure about the Pi 3, but the CHIP should not have a hard limit on the number of clients.
Yes, since the bandwidth is so narrow, we delivery only one file at a time now. We've been doing this for awhile now. I'm not sure what the guy in the Youtube video was downloading, but it may have been an unusual circumstance.
At most, we broadcast 20MB of content per day. In Librarian there may be an indicator that shows the bitrate. It is located in the first tab of the Dashboard--I think.