It's a good start to a tournament list, it just needs optimising.
HQ:
Your overlord should be loaded out with sempiternal weave, mindshackle scarabs and warscythe. This will make him a beast in challenges, also he can tank some wounds with his 2+ save, this load out comes in at 130pts.
The only time you need to bring a harbringer of despair is with deathmarks, but you shouldn't need to bring any at 1000pts, so
id say remove him and free up points.
Troops:
If you're going to put your warriors in night scythes then 5 man squads is enough, but if you wanted ghost arks then 10 is the correct number, adjusting squad sizes to account for characters and the ghost arks capacity.
Fast attack:
3 lonely wraiths won't be that much of a threat, and if you can't hide them well, then it's also an easy first blood. My advice is to either remove the entire unit, or beef it out to a 6 man unit, but definitely get rid of all whip coils, not necessary.
Heavy support:
2 annihilation barges is okay, but with the saved points I think 3rd is an excellent choice

. Nonetheless annihilation barges are an excellent choice, probably still one of the most cost effective units in the game.
I hope this helps
minimanj