I've done a fair amount of playing around with UV photography. In my opinion, the best overall summary and examples of it are on Bjoern Roerslett's site.

You do not need pricey optics or special film to do UV photography. I typically use the apo Nikkor process lenses, which have almost exactly the same focus in the near UV (350-400 nm) as the visible. They have quite good UV transmission, as do many of the EL lenses (which, however, are not apo but are very inexpensive).

I have used a 403 filter, it's fine. I also have a 325 but haven't played with it yet; it's set aside for a winter solar project.

For film, I have used mostly polaroid type 55 and 665, because it allows me to check exposure quickly. Actually there is almost no exposure compensation when you use old, traditional b&w films with a 403 filter and the lenses that I mentioned.

Bottom line is: just look at the filter cutoff, the film sensitivity curve, and the glass cutoff as a function of wavelength and all will be clear. Obviously the UV intensity you record will be a convolution of those three things.