There's no option to put the viewer on the left. It can only be on the right or on the bottom.
Grid lines are only available in Details and Power modes. (Is there any reason to have gridlines in other modes where there are not multiple columns per file?) You can turn them on via Preferences - Lister Display Modes - Details Mode and Power Mode.
Special "system" folders such as My Computer and Desktop are an exception since, currently, Opus uses components of Explorer to display them. In the case of Desktop, go to /desktopdir instead of /desktop and it will be displayed as a real directory instead of the merged Destop system folder.