Hi Cluster,
to IceInspace!
You may be lucky getting the Nikon to focus at prime focus, but you won't know until you try it. Of course afocal (shooting through an eyepiece, with the lens on the camera) is an option, but won't give you the results you're after for deep-space imaging.
What did you primarily want to photograph? (moon/planets/dso's)
The techniques and equipment needed can be quite different for the different types, and various amounts of money need to be sunk into it no matter which you choose
It's a long slippery slope, I hope you're ready for it!