Question on Group Postings and Main Community Stream

Hello... I'm considering creating GROUPS for the main areas of interest of my site users... and encouraging all STREAM POSTS to go through the appropriate group.

Couple of questions on this...

a) If the group is OPEN then posts made on its stream will show on the main Community stream?

b) If my users forgot to post from within the group (which I'm sure they will!) is there a way for SuperAdmin to 'move' a general Community stream post into the right GROUP?

Thanks for any comments on this!