Fallen Bastila... Again...

Hi all!

I know this question pops up constantly, but here I am...

I really want to use Bastila (Fallen), but I'm a bit lost as of how...

Emperor Palpatine - Leader (no Traya, so...)
Bastila (Fallen)
Darth Sion
Darth Nihilus
and...

First off, is Nihilus worth it, here?

As as for 5th, who should I use? Sith Assassin, for the TM gain? Thrawn, because it's Thrawn? Sith Trooper, for another taunt? Something else, something outside the box?

Cheers, everyone!!!