Thanks for the responses.
A Daemon prince and some oblits are definitely on the list to get, once i figure out which models i want to use, and what conversion work is required! (6mm scale converting =

)
I totally understand the wanting extra activations. My problem just now is being fresh to Epic i am slightly limited in model availability. Spliting the Decimators may require an army re-think that is beyond my current model collection (for now!) and my worry is i end up with one of my garrison formations being the BTS. Sounds like the double deci's being the BTS have some plus points though so will try them out together...
I didn't realise people didn't rate the daemons - i've found them useful in boosting smaller formations so far. I started re-writing the list without them, but on reflection it feels slightly wrong playing chaos without them. I think i'll keep them in for now, try a few games more and pay closer attention to what impact they actually play.
List re-jig
1 x retinue with havocs (garrison)
1 x retinue with noise marines MoS (garrison)
1 x retinue with 4 x rhino and supreme commander
2 x Decimator BTS
5 x Terminator DemonPact MoT
1 x Chosen retinue with 2 x rhino DemonPact MoS
5 x Raptor
1 x Feral Titan
1 x Hellblade flight
6 x lesser daemons
3k exactly
I can garrison the 2 big retinues forward in mutually supporting locations, while the chosen and rhino retinue can set up to either run a flank with raptor support, or split as required. Deci's to go straight down the middle linking up with garrisons.
Not totally sold on the Noise marines. Tried them once and just found myself wishing they were havocs. Will give them another go and if i don't feel any better about them they'll get a repaint as extra havocs!
Did consider chopping noise marines and daemons to fit a 2nd Feral in. But 2 x Decimators AND 2 x Feral Titans seemed quite unfriendly to play against, so resisted... for now.
steve S