Wordpress and multisites, the rigth choice?

Wordpress and multisites, the rigth choice?

I'm about to start a website, for a non-profit organization, and I need it
to be a multi-site platform. I do not know Worpress but I know there is a
multi-site option. Thus I'm wondering if Wordpress is the right solution
...
So here what I need to support :
[1 platform, 1 community]
a single user base, and SSO (1 login to every sites)
[several sites, several looks]
each site needs to have his own style (colors, font, images... basically
only css imo)
[an accurate permission system]
each site needs to have his own administrators (could be 1, or 2 admin per
site). Each admin could only manage is own site and should be considered
as, more or less, a regular user in others sites.
each site should has his own usergroups, and admins of the site should be
able to manage usergroups and add / remove users. Usergroups need to have
permission to view / comment / post content.
I'm aware it might not fit all my needs, but I just wondering how
difficult is it to achieve that using Worpress : do I need to add tons of
modifications or plugins ? Is WP not the best choice to achieve that ?
Thanks for your help.