1-2 Hq
0-3 Elites
2-6 Troops
0-3 Fast Attack
0-3 Heavy Support
Any number. It really just has to do with how many points you are playing.
Using the Standard force organization chart you are allowed 2 HQ choices.
Necrons
You can't.
Following the compulsory list, 2
In warhammer terms TAU is a young yet sophisticated army which includes kroots and fire units. Personally I believe Tau are the best with Eldar in warhammer 40k.
The new apocalypse allows you to ignore the army list, and in so doing have more than 3 Elite choices per army.
A Codex: CSM army that uses only units with marks of Khorne? I would use either lots of template units or a heavy gunline.
If you are serious about Warhammer 40K you can only play Orks.
3 units can be chosen from your elites....however some codex have rules that ignore or alter this rule.
No new Warhammer armies come out or ever will come out. The ones released will stay released. If a new army came out it would coincide with all the other armies' storylines and units and it will wreck the entire concept.
You'll find the answer in the Warhammer Rulebook or in the army book you are playing.
There is no set amount of 'men' required to play Warhammer, as it is a points and unit based system. Each character or unit of 'men' (Elves, dragons, Chaos Space Marines, Monsters... the list goes on) is worth a set amount of points. When you play a game or Warhammer 40,000 or Warhammer Fantasy, you and your opponent will agree on a certain points limit for the battle.You select units for your army, ensuring that the sum total of their points does not exceed the total agreed upon by the waring parties. The force you select also has to include certain elements, and these differ between then Warhammer systems.To play a Warhammer 40,000 game, you have to have a HQ (Commander type character) and two units of troops.For Warhammer Fantasy you must take a Lord, and two units of core.