Regarding tactics, the usual Dark Eldar strategy of throwing ALL of your firepower into units 1 by 1 until they dissolve entirely applies doubly so here, since if you don't kill them they'll just get. back. up.
Focus Fire Focus Fire Focus Fire.
Also, we equal or outrange most Necron shooting; don't be afraid to hide behind your 36" guns for a turn.
Annihilation barges should be an early target; they put out way too much firepower to be allowed to exist.
Lastly, and always overlooked, is play to the mission. If you get smashed down to two remaining models, but they're the only two models on the board holding objectives... YOU WIN.
When it comes to your list;
Looks fun. I'd ditch the grav-talon on the bikes since all necron are LD10 and won't fail often enough to be worth it.
Talos with the HWB - Maybe swap for Heat Lance? Since Cities of Death is generally cluttered with little long-range LOS, turning corners into melta/lance range is always more effective than wasting turns trying to get angles on vehicles that will get cover saves.
Best of luck.
I dedicate these deaths to Odin Allfather, Spearshaker, One Eye.
Fleet Shadowmaker - Kabal of the Dying Sun; Cult of Marrow Excised; Coven of Lambent Hunger
Sons of the Last Breath - Chaos Space Marines
Host of Shattered Purity - Chaos Daemons