It all depends on your playing style, some Chapters focus on firepower while others in long range weapons, some in short range weapons, others in close combat. Read up on the armies, experiment a little, then you'll find the right army for you.
It all depends on your playing style
Of the list that you have provide, the marine corps infantry is the best.
Yes.
No. You can however use lesser demons and demon princes in a Chaos Space Marine Army.
Equivalent to a full bird Colonel in the US Army.
Definately a Demonhunter Grey Knight.
Space Marine Tactical Squad (includes 10 Space Marines) Space Marine Combat Squad (includes 5 Space marines) Space Marine Rhino Space Marine Scout Squad (includes 5 Space Marine Scouts) Space Marine Assault Squad (includes 5 Space Marines).
hell no the army is fine but the soldiers in the army compare nothing to the best out their the marines no matter what the mos is.
space marine
the marines are the best snipers hand down
You must out shoot for distance and when close out cc them, 10 man tact squad with a pf would work. Using a Vindicator to back up tact squad a good idea to.
Look in the Space Marine Codex, that's what it is there for.