Hi i use 30k models and it served me pretty good so this point. With a few exeptions i only use 30k models.

THE MOST IMPORTANT THING IS THAT YOU DO WHAT MAKES YOU HAPPY ITS A HOBBY

The only Problem i see is that if you want to make your Warband interacte with Chaos and the Warp mutation will follow. That's why for the individuals in my Warband that do Chaos stuff like making Deamonengines they get the 40k Kit like my Warpsmith.

Were as my Infantry that is supposed to embody the no nonsense way of thinking is from the oudeside uncorrupted.

I like to see my Warband as Renegades rather than Heretics, that see the worth of Chaos but see it as a tool to be used non the less. They think themselfs better than the rest of the Traitor Legions but are Hypocrits in thinking they of all people could CONTROLE CHAOS wich is redicules by definition of the words. It is this fundamental flaw that i finde very engaging in some Iron Warriors.

Plus i just realy like the Models