For the Tag Search.... In the ACP, click on the Application tab at the top of the page and click on Gallery Options towards the bottom left column. Next towards the top center click on the Block Options tab. Uncheck Show Tag Cloud and save changes at the bottom.
Okay, I'm not sure if there is a UI in the APC to remove the field/option to add tags to an image so if you hear differently please use the UI option. If not, you need to edit the template xengallery_media_edit_fields.