Recommend the appropriate theme options and whether to multisite?

Hey there. I hope you are doing well. I am looking for recommendations on theme selection, and advice on whether I should multisite.

First, a little background. Second, my help requests.

BACKGROUND

I am trying to set up several work areas for international collaboration. Each could have a different theme but all would be all under one site name. In other words, eventually I want to have areas for things such as language groups (a site for kreyol, for bhel, for french), interest groups (our board, our staff, our supporters) and probably other areas as well. Someone working in the Bhel language would be able to access and to work in the Bhel section, but could not access the Board section without being a Board member. We want to be able to hold virtual meetings, store documents, collaborate on projects and hold discussions.

I am familiar with setting up and using WordPress, but have never used multisite. When I have been experimenting, I I set up a subblog and used it to develop the main blog. We can try multisite, but I do not want to do something too big for my talent.

REQUESTS:

1. Do our goals sound like they would fit better under a multisite setup or could we do it with catagories and subblogs?

2. What theme would you recommend for hosting hte kind of functions described (discussions, forums, archiving, collaboration)?

THANKS

I appreciate your help and look forward to hearing from you.

/Steve/