The USB hardware (ignoring  v3 and later) 


Lines should be equal length with 90 Ohm diff. impedance
Each wire should be terminated to a  45 Ohm transceiver

The 5V supply is just convenience
It is not related to signalling (which works at  3.3V or 0.8V)
It is specified with 5% tolerance (4.75..5.25)
Most chargers run a 5.3V or even a little more

Devices report presence with a 1.5k pull-up resistor (to 3.3V)
The host side pulls down with 15k.

Cable length is limited to 5 meters

The chain is limited to 7 levels all-included (i.e. 5 hubs)