The rule of thumb is: 5 Mbps (5 megabits per second) download speed and very little upload speed per box.
It is useful to add a reserve to this minimum. To be on the safe side, we recommend at least a "30/10" connection, especially if you have 2 to 3 boxes.
If your Internet Provider specifies "50/50" or "100/10", this is more than enough to have 5 boxes running at the same time and surfing the Web, sending emails and download a moderate sized file at the same time. All this can be done with the same Internet access.
Note: e.g. "50/5" refers to 50 Mbit/s download and 5 Mbit/s upload speed.