Welcome to the Dark City! It is a fantastic resource, and there are some really talented people here, from painters and modellers to tournament players!
Honest advice right now for just about ANYONE playing 40k, not just dark eldar: Plan on using allies.
Seriously, it's the game right now. Mixing and matching allies is all the rage. Up till recently, I'd have said that if your opponents generally don't use allies, you may be able to get away with staying pure, but with the latest and greatest space marine stuff that came out, I don't really think that's accurate any more.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~If you're not super worried about being overly competitive and would rather stay pure DE, I'd plan on bringing some toughness in the form of a covens formation like the grotesquerie. Alternatively, another guy on the forums here claims to have had some success going super MSU strategy(he said he got Best DE at the Las Vegas Open).
Basically, he only paid for as many minimum units of warriors as necessary to get raiders with dark lances and venoms. So something like this for an 1850 list:
2 CADs
HQs:
2 Lhameans in Venoms w/dual cannons 150
Troops:
6x 5 Kabalite Warriors in venoms w/dual cannons 630
6x 5 Kabalite Warriors in raiders w/ dark lances 600
Fast Attack
6x Raiders w/dark Lances 360
Heavy Support
1 Ravager w/Disintegrator cannons 110
TOTAL 1850
You can see the theme and apply it to whatever points value you play at. At 1850, the list above has 8 venoms, 12 raiders, 12 minimum sized squads of obsec warriors, and a dissie ravager. (24 obsec units when you count dedicated transports)
Often, people fall into the "upgrade trap", wanting to run max-sized squads in raiders with all the options. But those people end up having 2 raiders, 3 venoms, 2 Ravagers, and a jetfighter. DE lists like that get eaten alive in the current meta. You need as many vehicles as possible if you're staying pure and not using coven units.
Welcome back!