All of the Hasselblad bodies are pretty much the same in the 500 series (the later ones like the 503 have TTL flash capability).
For starting out, I think the 500 C/M is very good. It's the same as the earlier 500 model, but you have the option to change/replace the viewing screen yourself (as opposed to having a repair shop do it for you). The screens and mirrors in the 500 C/M are also brighter than the earlier models.
An 80mm 2.8 lens is great to have. The earlier ones are chrome (silver or black) and use Bayonet 50 size filters. The later ones are a bit larger and are marked CF (there are also CFi and CB versions); these use Bayonet 60 size filters.
For backs, the A12s are very good, and there are several variations (the last have a built-on holder for the dark slide). Avoid the earlier "peep" backs, as they can give odd spacing on your film.
Most of the cameras you will find will have the waist-level finder, which is ok until you're outdoors in the bright sun. Look for a 45 degree prism finder (don't spend your money on the metered ones). At the store I work at, a Hasselblad 500 C/M in good condition with an 80mm lens, an A12 back, a waist-level finder, and a 45 degree prism usually totals to about $700-800.
Try to get your camera from a local dealer so you can check the camera yourself. Also, try to get as late a model of the body and back as you can. Hasselblad uses a date code as part of
their serial numbers on the body and backs:
V H P I C T U R E S
1 2 3 4 5 6 7 8 9 0
Example: a serial number such as 10ER8999 tells you that the part was made in 1998.
There is also a date code on the lenses, but they can be tough to read.
Things to check on a used Hasselblad include:
The lens: should have no excessive scratches on the front element and should be free of
dust and fungus. The focus ring should feel smooth when used. The shutter speeds
should sound progressively faster as you change from 1-1/500th. The aperture diaphragm should be free of oil on the blades. The lens mount should be free of dents and gouges. The
lens should attach and remove from the body securely and smoothly.
The body: should have no gummy light seal foam, and the mirror should be free of
scratches. The film advance should sound and feel smooth. The rear shutter baffle should be even when closed and have no gaps.
The back: should open and close smoothly. The film insert should be free of scratches on the film rollers and should feel and move smoothly. When attached to the camera, the back should feel secure, and there should be no gaps visible between the back and the body.
Ideally, the dark slide should have no dents or bends and should be easy to insert and remove. Also, the film insert and the back should have matching serial numbers.
There is at least one Hasselblad compendium available that will tell you all about the various models, lenses and accessories. I don't remember the exact title, but if you do
a search on google, you should find it.
Hope this helps