Fuse with as many thralls and believers as you can. Shoot for the perfect mix of class features, ability scores, racial modifiers, HP Sums, PP Sums, etc...
That's exactly what my signature character does...though, originally, he was only a Thrallherd fused with two thralls and all his followers. One of the thralls is a Metamind so any fusion is active 24/7.
This was until I realized that I could piggyback thralls off of thralls, and now he uses the "
villiage of thralls" build. However, I haven't updated him to compensate for that (which is why I haven't posted him yet). Though, I should also consider doing the summon mirror mephit and simulacrum to fuse with additional monsters for powers (I probably wont though because that will be too much work and hes far too powerful as is).
I was always fond of getting into thrallheard as a Kalashtar... gotta love racial PLA's
Yup. Any 5th level Kalashtar with the prerequisite ranks and feat can enter the PrC.
Honestly I don't see the point in using a Kalashtar over a Human (other than power link shards and the like). Although Kalashtar get mindlink for free they also lose the feat that humans get which could be used to take expanded knowledge (mindlink). So in a way, it doesn't matter. I guess it depends on whether you want a few extra skill points or power points.
I would rather be a human Telepath, that way I free up the feat and have access to the power anyway; in addition to the necessary power 'schism' at 7th level, which I won't have to take expanded knowledge to obtain. So it theoretically saves two feats...depending on the build.