USB Type-C will be fully backwards compatible, it will run the USB spec
all the way back to USB-1.0 (ie: it’ll run USB-2.0, USB-3,0 and
USB-3.1). In addition it will run several other specs like HDMI and
Lightning so you don’t need to worry about compatibility, and for the
port, you can’t fit a USB-A connector in the form factor of USB-C,
you’ll need "adapters" for the transition stage.