New User - Questions regarding PzC

[jckerr4]

Thanks Foul!
Heres another question if you don't mind.
If I choose one game, say Kharkov 42, will I be able to play other scenarios like Stalingrad or Kursk. I am thinking that I will have to buy the game for each scenario. If this is the case, can you recommend a some of the more popular verisons. I would rather not start playing a version that is not played that often via PBEM in the forums.