1/ No, I would interpret that as meaning the device was drawing less than the standard amount. Check your power budget just to make sure, though.
2/ You need the edged-port so that when a phone is disconnected/reconnected, it comes up quickly.
When you reboot the switch (which shouldn't happen very often - many switches should be able to run for years without reboots), the edge ports are coming up faster than the uplink port, so the phones can't communicate with their DHCP/provisioning server.
I just had a look in the 5120 command reference and I couldn't see an "uplink fast" option for this switch type, so for a reboot of the switch, you may be stuck with having to configure all the edge ports as down and then up again after you perform any reboot.