I figured I'd give some general info for Series 4. Nothing spoilerish, just some basic stuff.

Summary

The film starts with Telos, in Atris' academy. Everything that has happened since the Exile first arrived on Peragus is told through a series of flashbacks, after which Atris tells the Exile to leave, and off everyone goes to Nar Shaddaa.

The first 40 minutes are really just setup for Nar Shaddaa, introducing the HK-50s, the Exchange, the Council, etc. Kane begins to become a Jedi once again, in order to take down the Exchange in the second half of the film.

Characters

Main Characters
Kane Dolan/the Exile
Kreia
Atton Rand
Brianna/the Handmaiden
Atris
Mira
Bao-Dur
T3-M4
G0-T0/Goto
HK-50s

Supporting Characters
Sion
Visquis
Zez-Kai Ell
Hanharr
Twin Suns
Zhug Brothers
The Champ
Vogga the Hutt

And that's about it. I'll update this post if I think of anything to add. If you have any questions, post them here or in the Hexology thread on the KOTOR Movie Forums.