I was obsessed with warhammer fantasy last month and found warseer...so here I am!!!

I want to start playing warhammer fantasy and I am thinking of making a warriors of chaos army!
Since I am very new to the whole stuff of the game I want to make some general questions here!
My army will be 2000 points since all games in my local stores are near this value.

1)Are hellcannon and warshrine really important for a competitive army of woc?(I really like the whole dark knighty theme in woc and would like so spend my points for warriors,knights,skullcrushers)
2)Is army general worth all the points it can get usine the available choises?(for example lord of chaos 340-360 points with mount + mark +magic items,or deamon prince around 480)
3)Heroes worth their points in general?Or what is more efficient, a hero or let's say 3 skullcrushers or 3 dragon ogres?(i know it may have to do with playstyle,i just ask for a more general opinion)
4)Marks of Chaos gods:
-Any summary please on how the actualy doing in live action?
-A unit with a certain mark ''has'' to be painted with the colours of the appropriate god?
5)Any advices-guidance you could give me for the army i want to make (specified in 1) )?
6)I have a Deamon prince (old one,bought around 9 years ago more like toy,no clue for the game back then).Should I stick with it for army general or would it be better to come with something cheaper and save more points for Knights,skullcrushers etc?

Sorry for many questions, but I see everywhere very different opinions and I am a bit confused.I want to make the right choises-steps in this game, (the reasons are economical also).
Thank you in advance!