Okay, suggestions for both lists:
Daemon Prince - Take off MoT, get rid of both powers and take Warptime instead.
Terminators - Generally not worth taking, best taken with a Land Raider transport. Alternatively, 3-man combi-weapon spam are a good alternative. As they are, they're quite expensive and not really very tough. Mark of Slannesh gives them a boost against I4 MEQ, LCs might be worth considering against higher toughness Plague Marines.
Just a few thoughts. Not sure how you are for what models you have so I tried not to change it too much (in composition, at least.)
Troops: Get rid of Daemonic Possession on ALL the Rhinos. It's not worth the points on a 35pts vehicle...
Thousand Sons are fine - I'd drop the Personal Icon though.
Berserkers - drop meltabombs
Plague Marines are fine - I'd drop the Personal Icon though.
CSM - get as many special weapons into these squads as you can - double melta / double plasma in each. Take Icon of Chaos Glory in each squad in place of the Personal Icon
I'm not sure what Force Organisation Chart you're playing with, but the standard one only allows you to have 3 Heavy Support choices. You have far more than this...
Defilers are better than Vindicators against Death Guard - S8 is all you need to ID them and the Battlecannon can do that easily enough at a much longer range than the Demolisher Cannon. They can also be used to tie up squads in combat in a pinch.
Oblits are good, but you may have to join them together to solve the overcrowding of the HS slots.
Thanks for the input, good words, here are my thoughts as they come to me reading your review.
-I would consider dropping gift of chaos but im not so sure Id drop MOT and Bolt of Change, I still want him to be a threat and soak up more shots with 4 invul. save
-I actually did consider giving them mark of slaanesh even if just to get all 4 marks in there for fluff, and its definitely practical gamewise, ill have to make room for that.
-I cant disagree any more about taking demonic possession off the rhino, its too easy to get a stunned result and not be able to move for a turn, definitely cant afford that. Maybe Ill take extra armor, but if theres a shaken result, the crew inside cant shoot, am I correct? In the last game I played with this list (2000 pt) that was a big part of my game, shooting meltas out of my rhinos.
-Im using the personal icons to deep strike the obliterators and terminators so availability is key, I want to have a choice as to their location of deep strike. Meltabombs make the Khorne more capable in case a heavy tank rolls along I can be opportunistic.
-Yes, im not quite sure how force organization works in a 2500 pt game, the book wasnt very explicit, they just stated it be decided between players. Id assume just one more slot is available to each position (hq, troop, hvy, etc). How does it work in Ard boyz?
Thanks for the input, Ill post the changes.