WordPress Sentry user groups syncing into Gallery 2 / WP Role Manager

Hi there,
I'd like to start a blog with a Gallery2 attached to it.
Up to now I was running a copy of Gallery 1.5 locally.

I will protect the blog with WP Sentry http://wordpress.org/extend/plugins/wp-sentry/ so that different users in different groups can only see a fraction of the whole blog entries.

As I'm used to Gallery 1.5 I was thinking of using Gallery 2 as backend to store the pictures for the blog.
According to http://codex.gallery2.org/G1-G2_Comparison#Permissions_System I find G2 having the nice concepts of groups too.

My question now is:
Does WPG2 (3.x) automatically pulls the groups from WP Sentry into Gallery 2?
Or do I have to put the groups by hand into G2 and add each WP user to these groups (by hand) too?

What about WP Role Manager (another WordPress Plugin)? Do I need it for any of the mentioned actions?
I quite don't get what this post: http://gallery.menalto.com/node/75063 is about.
Would it make life easier for me anyhow? Or is it more overhead?

Overall the idea is to have just a single database with users and groups. If user a is in group Z he should see posts AND albums/pictures visible to people in group Z and neither pictures nor blog posting visible for group Y (with Users b,c and d).
Is it correct that one cannot login into Gallery 2 itself with the WP user? But one has to use WP as "gateway" to get access to the Gallery 2 part of the website? Can a normal user in this setup upload pictures too (if I grant him the rights ... How?)?

I hope my ideas of a blog can be achieved with the tools I chose.

Any other hints/suggestions?

Good night!
genbian