Dear Gary,
these are no dumb questions at all! All the cameras you mentioned are quality medium format cameras. All of them should be able to deliver high quality photos.
The Hasselblad ist a famous camera commonly recommended for portrait and fashion. However the 50mm lens that comes with it is quite short (would be comparable to a wide angle on your DSLR), so not optimal for portraiture. 80 or 150mm lenses are better for this. If you want to compare focal lengths between medium format and 24x36mm, just divide the mf focal length in half. So a 50mm lens has about the angle of view of a 25mm on a (Full Frame) DSRL, a 150mm is more like a 75mm and so on. I would only take the Hasselblad if the dealer has some longer lens.
Both the Hasselblad and the Mamiya C330 are 6x6 cameras, producing square images. Whether you like that depends on your taste. Of course you can always crop later (unless you shoot slide film).
The Mamiya C330 is a TLR, which has the benefit that there is nor mirror slap, so less vibration. Also, the screen image does not black out while doing the exposure. The C330 was the last model of a long line of Mamiya TLR cameras, so it is the youngest and most sophisticated of the Mamiya TLRs.
The RB67 is a 6x7 camera, offering a slightly larger negative than the Hasselblad and C330. Also well known as a workhorse of fashion and portrait photographers.
The Mamiya 645 has a negative format of 6x4,5cm, so quite smaller than the other cameras. But the camera itself is also smaller. Lenses are of high quality too, but the other cameras may deliver even better image quality simply because their format is larger (However, when you crop the images of the Hasselblad or C330 to rectangles, this benefit is lost since you end up with a 6x4,5cm frame as well). The Mamiya 645 is also the camera that should be most alike to your DSRL in handling. The other cameras have a waist level finder, where you can look at the image on a screen (though you can mount prisms on all of them I think, not sure about the Mamiya RB67). You should be aware that the image that you see in the waist level finder is left-right reverse! If that is a problem for you, better buy the Mamiya 645 or look for a prism for the other cameras.
So in short, all of these are good cameras. Since you have looked at them in the shop already I think it would be best to have a closer look on all of them and look how they handle. Then choose the camera that fits your style of work best.