i understand your reasons on the background stitch, but these are my concerns:
you have 4 units with which to bring in the bulk of your army. 1 is an IC. one round of combat before you get the daemons coming in and that could be one chance gone.
the other 3 icons are in squads of 6 men.
the possessed squad in the rhino could find themselves in the same boat as the IC very quickly if they are the only squad up to the enemy in turn 2.
shooting/combat wise for all squads your opponent only needs to cause 3 wounds and he gets 50% casualties. furthermore if the unit breaks, because they don't have ATSKNF, they keep running. if that happens in a situation where your opponent gets turn 1 and has enough fire power, you could be starting your first turn with just your spawn on the field with little or no chance of bringing on the rest of your army.
i know you are basing this on the assumption you will have cover available, but you know as well as i that you shouldn't base lists on hopes and dreams
also, back to the fluff - two full 10 man squads is still reletively few chaos marines so that wouldn't be too damaging to the background