What to use: Community/Site or UserGroup for our requirement?

I think you can use a combination of User pages (public/private) and Sites/Communities/Organizations. The Liferay User Guide section Managing Users might help you understand relation between UserGroup and User public/private pages.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.