The Samyang is manual control - manual f/stop setting and manual focus. For astrophotography/nightscapes that's absolutely no problem. In most cases it lives on f/2.8 anyway
For post-processing, you need to get a lens profile to match your camera (5d mk2 + samyang 14mm), as by default, the Samyang has some 'moustache distortion'. Once you apply the lens profile, it evens it out nicely and gets rid of some vignetting in the corners too.
Easy to do though - it's just a bulk action you can apply once you've imported your photos. I do it in Lightroom.
After that, treat it like any other photo.