I think the best candidate for Ifurita would be Hinako.  Not that she learns
from everyone else, but she can kick almost all of their butts no problem.

Ukyo seems to fit Nanami a little better than Nabiki.  She works for her
money, has morals, and was away from her 'love' a while, and was reunited
a bit later in another land.

I think the three Tendo sisters could be put together as the priestesses
a little more easily.  Nabiki would be bringing her own brand of priestesshood
to the bunch, but that should be fine.  Akane as Shayla, obviously.  Miz
could be done by Kasumi, and Afura Mann, the thinker would be Nabiki.

Alielle would be Tsubasa or Azusa.

Tofu as Fujisawa.

Kuno as Katsuhiko Jinnai.

Londs would be Happosai (we never see Londs's dark side).

I suppose Diva would be played by Kodachi.

The two princesses would need to be new characters, and of course Fatora
would need to be a doppleganger of Ranma-chan for the body double plotline
to work.

This is all my opinion, and is based on my watching all of the OAV tapes
(dubs) last night right in a row.

As for who plays Galus, I can't decide between Ryoga and Mousse.  I think
Ryoga should, just because I cut Shampoo from the cast ;^)

...Brett