Grid's currently not an option yet.
layout.xml is all that's needed at the moment. The next version of RetroFE will contain the ability to select 4x3, 16x9, etc. based on the monitor settings. That way if a theme supports multiple layouts, RetroFE will automatically select the right one for the monitor aspect ratio.
I think it currently supports manufacturer and developer as separate tags. If the developer tag is not available, it will use the manufacturer information for that field.