New player with some questions about army composition.

[Jnx]

Greetings. I'm about to start my third army (well fourth one but the first one is sold already) and you may have guessed already that it's dark elves. My other armies have massive model counts so I want an army which doesn't take 3 hours to deploy. This is some sort of a brainstorm for what to start with. I was thinking of something like this to get me quickly to the field

Dark riders
Dark riders
Cold one knights
Cold one knights
War hydra

Model count 23? Now that's something. Would that kind of a list make any sense at all? I'll probably love the dark riders because I love my pistoliers too. If this is viable, what hero choice would be fitting? Master on a mount? Beastmaster with manticore? I've already done a sorceress so to get her to the field maybe the basis of the list should be more like

Sorceress
15 corsairs (or 20?)
Dark riders
Cold one knights
Cold one knights (or blackguard?)
War hydra (I just want this one )

How much tanking capability is needed as DE? With my empire I run 2 x 30 swordsmen, they hold well. Are 15 corsairs enough or does one really need 20 or 25? Or should one use warriors? Fully mounted list really tempts me but I love some of the groundpounding models.

So what are the musts and must nots of DE? How should I start with a relatively low model count? (My empire army normally fields 150+ models, Imperial guard isn't much better)

[No one]

First: Welcome to D-net I hope you'll enjoy your stay here, if you're interested in tactics then check out DRAICH (stickied at the top of the tactics forum).
about your list:
all cavalry (exept the hydra) is very viable (I have a similar list and it works quite well though I run one unit of CoC's and shades with GW), first you should include a or two unit of harpies (5=55points=dirt cheap warmachine hunters and screeners) and DR are nearly always used in units of 5 with musician and RxB's.

About tanking capability: DE don't have many units cheap enough or though enough to hold a charge reliable (exeptions would be BG, spearelves and khainites with a cauldron of blood nearby)

A good DE list should, IMHO, include the following (although some very viable lists don't include any of these):
-1+ unit of 5 harpies
-1+ unit of 5 DR with mus and RxB's
-the ring of Hotek(unless you use magic) on the CoK/BG champion
-a Hydra! (they're cool and way too cheap for their power)

for other examples of lists just check out the list forum, about modelcount: There are very good list with high modelcount and also good list with a low modelcount, it's up to your own preferences.