Hi Trevor,
It really depends on what you want to image and how you want to do it.
If you want to do widefield images, a DSLR with a standard lens on a tracking mount will allow you to get some great shots of the Milky Way.
Prime focus photography with a scope will allow you to image Galaxies and Nebulas because you are using a longer focal length.
As for the exposure time, anywhere between 4min-8min is probably the ideal exposure time for long expsoure photography with a DSLR. You will want to capture as many exposures as possible in an imaging session to get the best results.
Pretty basic but I hope it helps.
