You don't need the mastery level on the Daemon Prince; you'd have to take your only power from the Tzeentch table (I don't ever give my Daemon Princes mastery levels). Replace with wings. Makes the
DP a whole lot more killy, what with zipping around the board.
I would take off
MoT, it's practically useless on anything that doesn't already have an invulnerable save (that also means getting rid of Icon of Flame, which is ALWAYS useless). Replace if possible with
MoS and Icon of Excess; the mark grants +1 to initiative, so if you get into combat, you hit first, and that is excellent. The Icon also grants a +5
FnP which is wonderful. You don't need
VOTLW either, it is limited in terms of usefulness.
Hellturkey is good, only one is perfect. You won't get things thrown at you across the table with the singular one.
I'm a big fan of Maulerfiends, so this breaks my heart to say... but take it out. You have pretty much no heavy firepower. So I'd recommend a group of Havocs, either with auto cannons or missile launchers. With auto cannons you're sending out 8 strength 7
AP 4 shots, and while missile launchers only bust out one shot each, they are strength 4
AP 6 small blasts, with an option to fire krak missiles at strength 8
AP 3 (they aren't small blast though).
I hope I've helped as much as I think I have.