Hi Justine,
Assuming that you are on Linux run ifconfig to check if you have a usb0 interface available. It will not appear until Reach has at least partly booted.
If you do, run sudo ifconfig usb0 192.168.2.2
Reach should now be available on 192.168.2.15
/dev/ttyACM0 that you see does not have console, it is used to send data. You can send NMEA position there by configuring position output to USB-to-PC option.
Radio telescope? Sounds awesome! Do you intend to use Reach to calibrate where the antenna is pointing at?