Howdy
Firstly Dark Elves are one of the most competitive teams, they have a lot of good units, a lot of great units, and a few broken combos that you should stay away from (if tourney style practice is to your liking, so should you attend one you wont be thrown out mentally at all the changes)
Things that people really dont like to see:
Biggest one, by a million miles are 2x Hydras. This will make people rage quit even worse then 2x Hell Pit Abominations or Steam Tanks. One is fine, why wouldnt you? 2 is nasty.
Too many shades
Too much repeater crossbow spam.
Cant remember exactly items off by heart, but I know the sacrificial dagger is a big one
Cauldron of blood can get a few issue combos.
Dragon egg or somesuch
The last 4 I mentioned are not so bad
All the units that you mentioned having will enable you to get started with a fairly decent force.
I'm assuming a regiment is 20 models
If so, for your army I would be looking at something like:
Lvl 4 Sorceress
Battle standard bearer with defensive items
20+ spears with FC, dont know DE banners but the Razor standard (for armour piercing killyness) or banner of eternal flame (flaming magical attacks for regen monsters and ethereal units) seem like good choices, and both capitalise on high WS and I. Remember to make good use of your extra spear attacks which can use funky ranks like 7 wide 3 deep which would be optimal against steadfast seeking opponents.
10+ Repeater Crossbowmen -Banner, Musician, if they can take magic banner, eternal flame would be great
Group of corsairs with hand crossbows (this is more my personal taste as they have a decent amount of shots and are accurate, not as good as repeater crossbowmen, but better in combat and can stand in a battle line, stand and shoot giving a boost, otherwise most of their choices are good)
If its a decent blob give it full command, if in smaller units just a musician unless you want to boost your
If models allow, another unit of spearmen, 6 wide 2 deep could be a cheap choice for another deployment drop and as a supporting flanker. I would leave command at a musician.
Champions are after all mostly for challenging really tank heroes to get mauled instead of the unit.
5x Cold One Knights - These guys cannot break ranks, so you either want to go hammer (powerful unit) or cheap to harrass, support another unit with some extra combat res or hunt shooters/war machines. I suggest the cheaper option.
Block of Black guard - Full command, magic banner. These guys kick ass. Yup. They will be a pretty good target for the enemy though, as in for shooting, war machines and magic attacks.
I'm not 100%, but i'm pretty sure their stat line boosts the DE strengths, but retains their weakness.
Explained, Dark Elves are Expensive, and easy to wound. Toughness three an what, maximum armour save of 4+ means they are not that hard to kill.
However they have even MORE Initiative, WS and they hurt, big choppy weapons of some sort.
I would look at a magic banner that can protect the unit from shooting/magic, such as one that provides a ward save or something
To expand on your army:
Hydra (JUST one. They are awesome. Really)
The outrider dudes on horses, just a small unit or 5.
Maybe another hero
Maybe another box of dudes to split between your spears and crossbows, just dont overload on the bows.
Shades - These guys are awesome. Their deployment rule makes them amazing, you'll see when you play a game and you place them somewhere really annoying, like next to a war machine or behind the enemy battle line to rear charge.
And the most important one, whatever you like!!!
Just my couple of ideas
Peace
