Hey, I'm going to go through your list and explain the problems with it, if anything I say doesn't make sense (or you just disagree) I will be happy to elaborate, this is of course your list and you can do whatever you like. My comments may seem harsh, but it is just easier and clearer if I am brutally honest in my critique. Nothing personal.
HQ
Archon
Agoniser
Shadow field
Soultrap
Ghost Plate Armour
Combat drugs
Haywire Grenades
WWP
The Ghost Plate is typically an unneeded expense as you have a shadowfield and it won't save you once that's gone. The Soultrap + Agoniser doesn't work as already stated.
Archon
Huskblade
Soul trap
ghost plate Armour
Combat drugs
WWP
2 Archons is OK, but if you are doing this you need less upgrades, again drop the Ghostplate.
Troops
10 Dark Eldar Warriors
1 x Splinter Cannon
Syrabite
GhostPlate Armour
Agoniser
This is not an assault unit primarily and so doesn't need an agoniser or ghost plate. If you try to use it as a primary assault unit you will be dissapointed. It does need a raider and posibly a balster. The raider gives you mobility and the blaster adds firepower.
20 Dark Eldar Warriors
2 x Dark Lances
Blaster
Syrabite
Agoniser
Ghost Plate Armour
Blast Pistol
Dark Lances are heavy weapons this means the squad cannot move and fire them. If you are moving at all you are therefore wasting your dark lance shots. The Blaster is a medium ranged assault weapon, it requires you to move. The Blast Pistol is a point blank range weapon which you will never ever use in a foot based squad, but really really requires you to move if you ever want even a half chance at using it. These things synergise poorly.
Ghost plate is not useful here as you will take wounds on things other than the sybarite first, typically. The agoniser is not useful as this is clearly not an assault unit.
I'm not sure what this is for, but it doesn't matter it can't do anyhting well. If you let me know what you want it to do I may be able to suggest a set up that will work.
Elites
Hekatrix BloodBrides
Razorflails
Hydra Gauntlets
Shardnet & Impailer
Syren
Blast Pistol
Agoniser
You don't want to mix your specials they end up being less effective as they do different things. Shardnets particularly don't play well with others. Razorflails and Hydra Gauntlets are both for damage output, Shardnets are defensive. 1 Shardnet does little on it's own, whilst 3 turns of units. Equally a Shardnet contributes nothing to a unit meant to kill stuff, decide what this squad is for then switch out to homogenous weapons.
The balst pistol is a waste of time, you will almost always fleet instead. If they don't ahve a raider they are dead.
5 Incubi
Klavex
Bloodstone
Onslaught
The bloodstone is a gigantic waste of points, Onslaught is nice but a bit pricey and not terribly useful on a unit that is already this killy. This squad needs a transport desperately.
How many?
Fast Attack
5 Hellions
Helliarch
This unit is OK, maybe add 1 more Hellion.
have worked out - for an 1800pt list all i need to add is another warriour squad - shredder, Splinter Cannon
Shredders are terrible as they have no AP, blasters are flat better, heck a Splinter rifle is often better.
Void Raven (4 Necrotoxin Missiles, Night Shields, Flickerfield)
Necro missiles are an unnecessary expense.
change the Agoniser to an Electrocorossive Whip.
That would make your strength matter indeed.
Barely, you are still incredibly fragile as your units aren't in transports, so you are slow and easily taken apart at a distance.
True, but you also need your troop squads to be good.
and anti-tank S9 AP2 Shots
Not nearly enough you need a bare minimum of 14 (and that is low) functional Dark Light weapons in 1800, you have 4.
3+ wounding poisoned missiles with Large Blast!
Sound nice, not really worth it when you don't have enough stuff elsewhere.
Not yet, I'm afraid.