1.
If you look at the example in the documentation (http://www.solspace.com/docs/friends/group_entry_add/#examples), you can see this dropdown to display groups when using the Group Entry Add form:
<select name="friends_group_id[]" multiple="multiple">
{exp:friends:groups dynamic="off"}
<option value="{friends_group_id}">{friends_group_title}</option>
{/exp:friends:groups}
</select>
You could limit that list to group owners using the {friends_group_owner_id}
parameter (http://www.solspace.com/docs/friends/groups/#friends_group_owner_id):
<select name="friends_group_id[]" multiple="multiple">
{exp:friends:groups dynamic="off"}
{if logged_in_member_id == friends_group_owner_id}
<option value="{friends_group_id}">{friends_group_title}</option>
{/if}
{/exp:friends:groups}
</select>
2.
The private=""
parameter in {exp:friends:group_entries} should allow you to not show entries from a private group. In the docs: http://www.solspace.com/docs/friends/group_entries/#private
3.
See answer for #2. Commenting and interacting (I'm assuming editing?) with entries depends on the code you decide to put inside {exp:friends:group_entries}