I owned RB's for quite a while before going Hassy...the first thing to do is to get a complete CLA for the body and a Reseal/Replacement for both the backs *AND* the revolving adapter. Don't trust the seals on these pieces: even if they look new (unless you know of when they were replaced). They may work great and suddenly, after a film change, the back could start leaking light.
And, many people neglect to have the foam on the rotating back replaced.
2: If you get a prism, get the prism Model 2 (the newer one). The old one is a brick. The new one is almost a full pound lighter.
3: Get a bright screen ("Brightscreen" or "Intenscreen" or Maxwell screen). The factory screens are OK, but suck severely in low light.
4: Get a good strap and/or bracket and a good tripod. Trust me. I did 30min of "RB exercises" before every major, long shoot just so my wrist wouldn't hurt after a long wedding (YES, I *DID* use the RB for weddings...out of the studio).
5: Stay away from the 1st series of lenses. Get the C series lenses, at the least. The older ones have horrible contrast...and the 210APO is an awesome lens.
6: If you ever get the motorized backs, get the newer ones, where the batteries are in the back and not separate. The contacts on the older, separate units can become intermittent and give you hell.
7: Avoid the multi-piece, older WLF. The newer one-piece WLF is a ton better. The older one's have springs that fail and eventually won't open up correctly.
Enjoy your RB, avoid the Pro, get at least a Pro-S. The Pro-SD's aren't much more expensive than the Pro-S's and will allow the shift or fisheye lenses.