I found the answer to Point 1 above.
Mock Title: hides the selected row (for which this setting is done) and displays its child rows directly under its parent row!
Example:
Heading 1
Heading 1.1
Heading 1.1.1
Here if Heading 1.1 is made as Mock Title, then Heading 1.1.1 and its child rows will be shown directly under Heading 1
Hide Accounts: hides the child GL accounts, but does not hide the selected row for which this setting is done. This setting makes sense only for Level 4 Rows, as only they can have GL accounts, even though this setting is available for Level 2 and Level 3 rows also.
(Note: Level 2 and Level 3 rows will display this checkbox only if you first click on a Level 4 Row for which this checkbox is shown, and then click on a Level 2 or Level 3 row. Its probably a bug, because if you click on a Level 1 Row and then click on a Level 2 or Level 3 row, then this checkbox is not visible and anyway does not make sense for a Level 2 or Level 3 row.)
If both check boxes are checked, then the selected row will not be shown and its child GL accounts (if it is a Level 4 Row) will also not be shown. However, any parent rows will include the selected row's child accounts in their total value.
Still looking for answer to Point 2.