I'll repeat what the other folks have already said: Fateweaver is fantastic.
I'll give some reasons, though, instead of just giving an unsupported opinion.
Fateweaver's single re-roll per turn will help keep your
FMCs in the air, contributing greatly to their survivability. His ability to fire off an AP2 blast and beam each turn kills most things, and especially Termies. Finally, the Warlord Trait means you won't be killing your own models with the Warp Storm.
All in all, definitely worth it.
You should also try fitting in the Grimoire. The Grimoire will make one of your
DPs (or Fatey) invincible. Taking the Portal is a good move, especially when you only have 5 units on the board.
And finally...why the

do you have Tzeentch Princes who don't have Lesser Rewards??
EVERY Tzeentch
MC NEEDS the Staff of Change. +2Str for 10pts? If you don't take it, then I have some uncomplimentary observations to make regarding your intelligence!