There are countless ways to theme your force. Some prefer to pick a single chapter and focus on a certain set of abilities, others like to combine strange, disparate elements into a loose warband, and others will field them like a traditional space marine armor with all the armor and firepower that is not that different from the loyalists.
Here is the Battleforce Box
15 Chaos Space Marines
5 Possessed Marines
8 Khorne Berserkers
1 Rhino Transport
This will cost $110, or you can purchase the units separately for $165.50 with 4 extra Berserkers
These rely largely on your choice of chapter and patron deity.
Khorne units favor red and brass
Nurgle Units favor green and brown
Slaanesh untis favor purple and pink
Tzeentch units favor blue and gold
Take a look at the models you like and try to match them closely. There is a reason why these colors are chosen for certain models.
- If you want to field a "power specific" force, start buying up the specific units that correspond to that power. Nurgle units are tough, Khorne units are hitty, Tzeentch units have lots of different abilities, and Slaanesh units have some ammazing shooting
- The HQ units in this army are devastating. They can shoot, hit, and cast psychic powers with the best of them. The plastic commander kit is a good option since it lets you make just about anything you want.
- Armor. Chaos Land Raiders, Predators, Rhinos, and the infamous Defiler are great in this army. They have more options than their Imperial counterparts and should be included right away.
- Elite units like Terminators and Obliterators are also a must have. They add even more shooting and combat skill to an army that already excels at it.
Your army will likely be smaller than a normal Space Marine force, but your units will have more abilities at their disposal. Take advantage of their special skills and maximize what they are good at.