Ready-to-use image with no graphic interface and SSH on

[pfeerick]

Armbian is the one you're looking for: http://www.armbian.com/pine64/

SSH On by default
Lightweight
No display required

DietPi is another good option. Both DietPi and Armbian are perfect for headless / SSH boxes, and are both well configured out of the box. DietPi is nicer if you want a GUI later, as you can easily install your preferred desktop environment from the DietPi launcher. Longsleeps Ubuntu build is the other one I'd recommend - I don't know off the top of my head if SSH is enabled out of the box but I would suspect it is.