Clarrification on setup of sharing for dynamic groups

I could use some expert help on understanding the steps to configure sharing rights for different dynamic groups.

I'm using eDir and I have three dynamic groups - Teacher, Staff and Students

Right now I want
Teachers to have all sharing rights but external/public
Staff to have all sharing rights but public
Students to have no sharing rights at all

Can someone tell me how to go through the Share Settings, User Accounts, ?groups? in the Administration console to easily assign these rights to my 2000+ users? The documentation is confusing and seems to have me end up with all sharing rights turned on for all users and then tell me to turn it off under User Accounts, which requires touching each user or subset of 25 users at a time to configure rights.

I am hoping that the steps are not.
1.) Turn on sharing for the built in 'all internal users' group.
2.) Manually select all users in subsets a maximum of 25 at a time and CLEAR the rights that you don't want them to have.

I'd be in for a late night. Is there a better way? I'm loving Filr version 1.0 but I need easy sharing rights too.

Thanks.