Hi, I use the net profiler for profiling network bandwidth. As for what is good and bad there, AFAIK by default UE caps at 5 kilobytes per second, so if you use more bandwidth than that, this would be bad. Ofc if you increase/change that limit in the config files, then over whatever limit you set would be bad (and ofc the lower the bandwidth you use the better).
Don’t see what any of this has to do with multiplayer, those things depend on the target platform where you want your game to run.
As for physics and multiplayer, I’ve never really used it but from what I’ve heard physics simulation can be a pain in multiplayer.
AFAIK won’t affect your bandwidth usage any, but will lower the load on your GPU and CPU and I use them all the time.