1 - I think yes, there should be no problem.. but you dont lose anything installing first the update to 1.5.1... and will only take you 5 seconds

2. read this: http://www.joomlamusicsolutions.com/en/support/upgrading-music-collection-from-1-5-1-to-2-0-0.html

community allows frontend users to add content, basically, while non-community works just as 1.5.0 did: only admins add content

Thanks Germi.. sorry for the stupid question.