1)Daemons are too random,
BT gunline,
DA deathwing,
DA dualwing are on par with a good vanilla list like a Vulkan list.
A good
CSM, ravenwing,
BT assault list are about as good as a average vanilla list.
DA in power armour and a quiet
CSM list are worse than vanilla
2)God of War only does morale checks, no other leadership tests, this is often misplayed. You already have combat tactics which is the really useful half of the skill. This isn't his strength.
He real strength is being awesomely killy and yet hard to kill. He is still overpriced back away.
3)The advantage of the codex is that it is flexible. In terms of skills you have one special skill beyond normal marines, choose from
fleet
stubborn
combat tactics - choose to fail a morale check - this is great
all meltas and flamers are twin linked

- this is better
4) Chaplains make units fearless. Fearless is not a good skill in
cc in general, where the chaplain wants to be. SO essentially a chaplain and assault termies is the only good fearless unit.
5)All transport options are amazing in their own way. The key is how your whole list blends together. Really one drop pod is a good suicide unit, and a whole army of drop pods is strange but effective thing. Then rhinos are dirt cheap and can be shot from. Razorbacks are gun platforms.
6)Daemons no idea.
DA is definitely more expensive in terms of points.
CSM have cheap marine squads to keep the cost down but the good stuff costs serious points.