TABS, TABS Permissions View, Groups Dubts

Hello All. Thank you so much for beeing a growing community helping each other. 

I would like to change few things in the main tabs and for their permission view.

Where we see "Activity, Discussion, Groups, Plugins, Showcas, Themes" I want to remove most (Including Activity Tab). If possible, Activity Tab is only visible for Administrators. 

At Group Tab, and Others, I would like to remove the "tab All": Groups (All groups), Discussion (All discussions pages), etc... and redirect to "My TAB's": Groups (My Groups), Pages (My Pages)

The groups dubt is: How can I invite a user to a group that is not visible to (Registered Users)? 
The user Can't see the group. I need to change view permission to the group any time I want to add a new user to the group?