Before you jump into this new way of shooting, make sure this is what you want. 35mm and medium format are two very different ways of seeing. Since you've never handled a 6x6 with WLF, I strongly concur with Hikari that you get an inexpensive TLR or even a Mamiya 645 with an 80mm. Let me share some insights. I've been shooting 35mm as well as MF for many years. I bought my first MF--the Mamiya 645-- over 20 years ago and it still works & I still use it. I've also used many 35's over the years and currently shoot with an M3, a Contax 137 and more recently some older Canon equipment. I've found that 35mm is great for shooting action and taking photos of people in fast moving situations. I've been using my MF equipment (including my 500c) primarily for scenics (especially seascapes) and still lifes. My shooting styles with both types of equipment are very different and driven by subject matter. As you decide which way to go to rebuild your photographic collection, give a great deal of thought on what you will be shooting.
If you plan to continue the same shooting style that you had with your Nikon but now your going to use a Hasselblad, your in for a very rude awakening. Start by thinking 12 frames vs 35 on a roll. Decide about your processing. Do you do your own darkroom work or do you have it processed? If you do your own lab work, plan to invest in 120 reels & tanks. Does your present enlarger handle 6x6? Plan on getting an 80mm enlarging lens. If you send your film out, does your current processor handle 120 film? Don't get me wrong, processing 120 has been a lot of fun for me & I enjoy the creative process. I don't mean to discourage you either, but making this change and to not expect a change in your shooting style might be very frustrating. If you are moving from an auto focus and in-camera metering platform to one in which you focus manually and meter your scenes with an external meter, you will have to incorporate these as well into your shooting style. A Hasselblad is a great creative instrument with it's square format and slower pace but don't expect it to be a panacea for all your photographic challenges.
Didn't mean to muddy the waters, or deter you from your purchase but make sure you think through all the various different dynamics. If I were you (and of course, I'm not!) I'd probably purchase another Nikon, maybe an F100 with zoom for well under $400 and purchase a cheaper 6x6 (Yashica, Mamiya, etc) and see how it works for you. Then, after you've had a chance to handle an MF camera and like the feel and the outcome, by all means get that Hassey (but still keep the Nikon). Cheers!