Clone Group

Yes, it is. To clone a group, please add 'clone' => true to the group field.

Just in the group field, for example:

'fields' => array(
    array(
        'id' => 'group_id',
        'type' => 'group',
        'fields' => array(
            // Sub-fields here
        ),
        'clone' => true, // This is all you need
    )
)

You mean you can edit fields without touching code? If so, we have 2 extensions for this purpose: MB Builder extension or MB Template extension.

Regarding the text and image: yes, you can do that. You need to register a group which has 2 sub-fields: text and file_input (do not use any image fields here as they won't work for group):

$meta_boxes[] = array(
	'title' => 'Meta Box Title',
	'post_types' => 'custom-post-type',
	'fields' => array(
		array(
			'id' => 'group',
			'type' => 'group',
			'clone' => true,
			'fields' => array(
				array(
					'id' => 'text',
					'name' => 'Text',
					'type' => 'text',
				),
				array(
					'id' => 'image',
					'name' => 'Image',
					'type' => 'file_input',
				),
			),
		),
	),
);