How many kb/s are reasonable?

According to google the average mobile upload speed is 5MegaBits per second in the US.

So i go by a rule of thumb of max 1MegaBit per second. In construct 3 stats, thats 125kb's .

So for 8 to 10 players you should be fine, you can have half your bandwidth by changing the precision from high(8 bytes per value) to normal(4 bytes per value), or even low(2 bytes per value).

Further, you should really only worry about the host, generally your sending inputs to the host(minimal bandwidth) then sending x,y, and angles of each synced object to each peer.

Thanks. That's a good starting point!