[Dave T Hobbit]

If you are referring to the shepherd's crook usually paired with a flail then probably wire with green-stuff is your best bet.

If you are looking for a stave-khopesh then there is this tutorial; if you do not want the use Tomb King parts then 2mm plastic-card is easy to shape with a knife and files.

 

[Dave T Hobbit]

I am wondering what units I should choose? Are Chaos Raptors fluffy? How about Havocs?

It depends on your interpretation of fluff: the Rubric supposedly turned all non-Sorcerer Thousand Sons into dust filled shells with no real connection with reality, so fluff could be:
(1) Hardcore - All non-vehicle units must be either Rubric Marines or Psykers
(2) Warp Anomaly - time is funny in the Warp, so some of your units are pre-Rubric (as the Rubric changed the Armour form Red to Blue, this might involve painting units differently)
(3) Allies and Initiates - The Sorcerer leading your Thousand Sons has recruited (i) other Tzeentch worshippers or even (ii) mercenary units like Obliterators
(4) Uncontrolled Mutation and Unknown Magicks - some badly mutated Thousand Sons were too far gone to be affected by the Rubric, and some Sorcerers developed little known powers leading to an army where non-Thousand Sons use the rules for other units but fluff-wise are doing it by mutation or psychic power instead of jump packs and heavy weapons.

Depending on your fluff preference, the best units are likely to be:
HQ - Winged Daemon Prince
Troops -Thousand Sons
Elite - Chosen or Terminators
Heavy - Defilers or Vindicators (Obliterators if they fit your fluff)

Possessed, Dreadnoughts and Spawn are usually below average - although the randomness is very Tzeentchian.