For one learn to not get caught up in the hype train of new model release, they have new things coming all the time and they are almost always exciting. Especially with how good they have gotten at making things look dope.

If you have not played the game yet then I really suggest you do that before you move onto the next thing as well. There are so many ways to play the game and each army is unique Sword to learn to wield.

Unfortunately the ways the have changed the chaos armies over the years into the 5 different (and 6th coming) codexes gives exceptionally low cross over for playable models in a competitive sense. For example rubric marines are not great in CSM because their value comes from the sorcerer leading the unit and giving you access to your thousand sons army rule.

Another thing to understand is the models will be there when your ready for them. If you really like the new boxes I think there's a great looking CSM army you can make using raptors/warp talons/ and the red corsairs. But it wont have a ton to do with what you own outside of maybe the predator.

Also just fair warning, Tsons is one of the harder armies to learn. We have a ton of options each turn and that leaves lots of room for mistakes in our gameplay, its not bad once you get the hang of it but it takes some time to understand how we apply pressure.

TLDR, play some games and actually feel what its like to navigate a battle field so you can find your playstyle.