At least part of the question here is what you expect to go up against. If your enemies are going to be using a lot of vehicles, for example, your strategy is different than if you expect a mixed set of lists or infantry-heavy.
Probably your greatest weakness is lack of a Troops choice, since a single Troops unlocks the Patrol detachment, which is potentially quite valuable at 500 pts. Since you have to use either Spearhead or Vanguard, and Bonesingers are a bit on the weak side, I'd go with a Spearhead.
I'd take the War Walker with minimum guns-- 2 Shuriken Cannons to make use of battle focus, as well as two stripped-down Wraithlords. The War Walker will be pretty mobile, and Wraithlords are fairly beastly at low points values when anti-tank is rarer. Have one of the Wraithlords take a sword, 2 shuriken canons, and 2 shuriken catapults, and he can run up and smack guys while shooting. The second one will have to go without a sword for cost reasons.
For HQ, I'd take a spiritseer since it's cheap, has a full smite, can cast Jinx (the protective spells won't work in this army), and helps out your Wraithlords when near the enemy. Note that Spirit Mark is a malus-field, not a buff-field, so he needs to be near enemies to apply the Spirit Mark to them.
With the remaining points, I'd take a stripped-down Wave Serpent, to keep in the theme of only giving your opponents terrible targets to shoot at. The extra dakka will help and it will be a good mobile objective taker. Treat it like a tank.
Spearhead - 500 pts
Spiritseer with Protect/Jinx
War Walker with 2 Shuriken Cannons
Wraithlord with 2 Shuriken Cannons, 2 Shuriken Catapults, 1 Ghostglaive
Wraithlord with 2 Shuriken Cannons, 2 Shuriken Catapults
Wave Serpent with Twin Shuriken Cannons, Twin Shuriken Catapults
Any of these guys (War Walker, Wraithlords, Wave Serpent) could trade out their Shuriken Cannons for Scatter Lasers if you want them to be a backfield objective-sitter.
So this list has 8 Shuriken Cannons, 6 Shuriken Catapults, and some very scary assault capabilities from the Wraithlords. In terms of anti-tank, you're relying on your Wraithlords to take them down in assault, though eventually sustained Shuriken Cannon fire may kill something.
Most notably, you're not presenting the opponent with ANYTHING good for small arms to shoot at. They'll waste most of their firepower against you, and bolters in particular are hilariously awful against Wraithlords.
The downside is you're leaning a lot on those Wraithlords to do damage in assault, and if your opponent has a lot of AT or gets lucky rolls, you're toast.
If at all possible, getting a troops unit could help. It would let you take a patrol with a Warlock,
a decent-sized troop unit, a unit of Wraithguard, and a Wraithlord, which would probably be more balanced and effective.