I don't see any M915 commands in your config.g so I presume you must have them in your homing files. You can change R1 to R0 in your M915 command if you don't want to receive those warnings.
With just USB power provided you can communicate with the Duet and test the networking, temperature sensors, endstop switches and Z probe. If you have a PanelDue with a 4.3 or 5 inch screen, that should work too. But the 7 inch screen takes more power than most USB ports will supply.
