I believe powering the board through the DC jack is better. I have a WD My Passport attached and running permanently without any issues. FYI the adapter that came with the board I ordered had coil whine which may or may not be a problem for you. This is the adapter I use now. It can supply up to 3A when set for 5V output.
If SSH is not enabled out of the box, you can mount the image, and manually enable SSH before booting from it. You will have to symlink the systemd script in order to enable. You can also edit sshd_config.