DTP World Font Style Book is a handy stylistic reference, just so you can see what’s already been done but it doesn’t show full katakana sets. A good exercise is to draw three styles of Katakana: a calligraphic style, a Times New Roman style and a Helvetica style. What I mean by Times New Roman style is katakana that harmonizes with a generic Roman. There are lots of them and hard (for me) to tell apart. Then there’s the common sans serif style seen on every Japanese magazine, paired with a Helvetica alphabet. If you draw those three styles, you can get an idea of the conservative distortion that’s allowed.

Of course, you’ll have to test your fonts with Japanese readers to find out where you went wrong.