First let me say I envy your Questar! I've never had the chance to even look through one.
Now onto AP questions. Deep Sky Stacker (DSS) is a good place to start stacking your pictures. It handles the NEF (RAW) format that NIKON uses. Always shoot RAW. There are other better and more expensive software, but you can grow into that. Photoshop is also useful if you have access to it.
If you have any long lenses, try shooting night shots with those lenses before coupling the camera to the Questar. Even if you’ve just got the kit lens try some exposures with it to get a feel for night sky photography.
Not familiar with the Questar focusing mechanics, but I would be concerned about its ability to keep focus with a fairly heavy camera. Along those lines, the full frame D600 could be noticeably vignetted because suspect the questar focuser is not an optimum diameter compared to the full frame camera. Next, the adapter would need to slide “into” the focuser in order to focus the image. Many scopes offer a T-ring adapter that securely connects the camera to the focuser. I also wonder if you have enough back focus to achieve focus.
I hope another user lucky enough to also have a Questar will be able to answer a number of these questions.
Did your Questar come with a tripod?. At its focal length, you’ll need a sturdy tripod just to get a non-blurry shot. Also, you’ll need to use a remote.
Without a means to follow the stars, you’ll be limited to fairly short exposures, especially with the very slow focal ratio of the Questar.
If you have a local astronomy club, they will be a goldmine of information
I don’t want to discourage you, but there are some pretty good challenges on the path you’ve proposed.
Best advice... read, read, read. try something.... keep reading and try again.