Answer for Is it possible to give access rights for different items to different users/groups?

Yes, In QPack it is possible to assign different rights for different Items to different Users
Work Item Permissions are defined under the Group.
The Admin can give View/Add/Update Item permissions to Different Group’s Users
Steps to Follow:
1. Login with Admin User
2. Select Admin > Users & Groups > Groups
3. Select the Group to View
4. Work Item Permissions tab is selected by default
5. Select the Item from the Dropdown
6. Update the Permissions that are to be given to the Group users