The backbone of your army will probably often consist of Chaos Warriors, and that's not a bad idea at all. They are without doubt one of the toughest regiments with their high characteristics in Ws, S, T, Ld and A, in all the elite soldier for h-t-h combat, and remember that. The Chaos forces are meant to attack more that any other race and they sure have the units for it. With Chaos armour you can increase their survivability, but as with everything else it will increase their cost too, you'll have to decide whether you'll need the extra armour before each battle. The biggest threat to the Chaos Warriors are magic and warmachines, like all other regiment they move in large regiments and are very woundrable to cannons, stone throwers and the likes. The only plan you should remember with these is to get into h-t-h as fast as possible.
Another possible "backbone-regiment" are the Beastmen. For a fair price you'll get a regiment with toughness of 4, two wounds and usable Ws. They have relatively low leadership compared to many other regiments but you can counter this in many ways :
The Beastmen are affected by the infighting rule, and even though you ad a Chaos Character this might occur. There's not much you can do about this, it's a chance you got to take. A unit of Beastmen often benefit greatly from a banner that can be used to add even more protection. As a Slaanesh general you even can render them immune to psychology and break tests which makes for a very persistent unit indeed.
Minotaurs are very tough h-t-h troops with 3 wounds, good Ws and Ld. Their high movement should be used to get them into h-t-h as fast as possible and their ability to carry standards should be used to increase their otherwise low armour protection (6+). You should keep in mind that the Minotaurs feet on defeated victims after their first combat, this could be quite annoying to you but still very dangerous for your opponent if he should attack. If the Minotaurs are attacked while feeding they'll become frenzied. Remember that Minotaurs cause fear.
As a Chaos general you'll also have the best cavalry in Warhammer available. The Chaos Knights cost a lot but with save of 2+, strength 6 and 2 attacks they are worth it. Though the Chaos Knights can destroy most other units you should, as always with knights, be careful not to end up in h-t-h for several rounds, avoid multiple-wound- and unbreakable troops. Your Chaos Knights should be used to break smaller/weaker enemy units.
Dragon Ogres are the heavy cavalry of Chaos, and they're really heavy. 4 wounds and excellent S and T makes them an horrible opponent. Their disadvantage is the Ld and I so be careful of Ld based magic, as they are capable of carrying banners you might want to use get some protective ones. Often the Dragon Ogres can be fielded in small numbers just to draw the opponent fire away from your other units. The Dragon Ogres causes fear.
Many consider the Harpies to be too weak to field in their armies, compared to other Chaos troops that might be true, but not fielding them is a mistake. The greatest threat to Chaos are warmachines, with Harpies you can with a little luck eliminate this already in the second turn. Use them in small units, and preferable only to attack warmachine crew, when there are no more warmachines you can use them to prevent the opponents troops from making march moves by staying within 8 inches, either behind or at the flank of the unit.
Deamons
The Demonettes are another of the awesome cavalry units from the Chaos armylist. High Ws, A, LD and movement on the Steeds of Slaanesh. Get them into h-t-h as soon as possible as they only have their Daemonic aura as protection. Their ability to use magic is also a good thing worth remembering. Their high movement makes them perfect for flank/rear attacks, alone or together with Chaos Knights. The Demonettes cause fear too.
Bloodletters are, except for their T of 3, excellent fighters. They can not cast magic like other Deamons, but armed with their Hellblade they don't need magic. The biggest problem is to get them into h-t-h before your opponent fires them to pieces, juggernauts is a solution, but it's expensive. Because of their Hellblade they should be used on stronger (multiple-wound) units. They also cause fear.
The Pink Horrors are another good h-t-h unit
that split into two Blue Horrors when killed. They have a low T but that is acceptable
when they just turn into two new Horrors when killed. The Blue Horrors are quite good in
h-t-h too. They lack the Deamonic aura so they are very woundrable to missilefire. You
should use these troops to bind up the opponent, which is possible for quite some time.
They can cast spells, and even create more Horrors with the Tzeentch Firestorm. Pink and
Blue Horrors cause fear.
Greater Deamons
The Greater Deamons can make every opponent loose all hope of victory, often their appearance do more damage than they actually do in h-t-h. They can "easily" be routed though if you charge directly into large units with banners with battlemodifiers, and as they flee they'll be destroyed. Use them as secondary attack on units and to kill (special) characters. Their ability to cause terror should be used too, just by moving them within 8 inches of your opponent he'll have to make a breaktest. Some of the Greater Daemons have magical abilities, but don't field them for that reason, if you want magic you should field mages instead, Greater Daemons are primarily for h-t-h slaughter. Due to their HIGH point cost (low compared to their skill) you have to have them in h-t-h all the time to get results again, don't be afraid to loose them, you'll be surprised how much they can take. If you keep in mind that they're weak against large regiments then they'll be almost undefeatable.
Chaos Characters
The Characters available to Chaos players are very expensive but amongst the strongest in Warhammer too. You must always deticate your character to one of the four chaos gods and, depending on your choice, you'll get even more special abilities. As your characters have high T your worst threat is no-save-weapons and magic, if you can protect your characters from this you'll be able to defeat most opponents. Due to their high pointcost you probably wont have many of them, think carefully of which units you decide to use them in because you sure wont be able to have one in each unit. Beastmen as unitleaders are generally a bad choice unless you use the Lord character due to their lower Ld. Minotauer Characters are really good fighters but lack the Ld and Ws and are affected by the feed rule too. The Dragon Ogre characters, especially Lords, are almost unaffordable, but capable of defeating almost everything too. Centauer characters have high mobility and acceptable characteristics plus they are allowed to carry bows, compared to Chaos Standards they are quite expensive.
Your Standard bearer is quite exceptional as
he is a Hero and not a Champion as with other races. He's good characteristics and ability
to carry two magic items actually enables him to take part in the battles. He can be
fielded as part of a unit. He's clearly worth he's points so you should consider buying a
Hero, or two, less and fielding him instead.
Nurgle Sorcerers have a cloud of flies around them that negates magic within 6" from
lower level sorcerers and gives an dispel against spells within that radius.
Tzeentch have that 4+ dispel.
Slaanesh sorcerers can't be shot at or targeted with spells (goes for the unit too in the case of spells) within 12".
All sorcerers have very good stats and as usual cost lost of points value but they are fully capable of holding their own in a fight, and that's pretty exceptional for a sorcerer/mage. The Chaos Sorcerers have the ability to choose dark magic spells, make sure to take at least one spell since this gives you the ability to discard some cards to get more powercards.
General Tactic
Because your units cost so much you'll often find yourself outnumbered but that doesn't matter anyway. Keep the woundrabillity to warmachines/magic/missiles in mind and charge, that's the basic tactic. Use really fast troops with high hitting power so you use every opportunity to reach your enemy fast. Many just charge in and rely too much on their superior troops. This won't probably work against a good opponent since he'll soon counter-attack you with superior numbers, spells or warmachines. This means that the proper tactic should be to attack units that break real quick. Try to take out your enemy's artillery and spellcasters with the Harpies. You have loads of troops that causes fear so learn use that.