Hi,
1. Unfortunately this is a code issue for 'water content in unsaturated zone' gridded results (only the first cell along the profile line is actually used). I've reported to our development team so I expect it will be fixed in a future release/update. Meanwhile the workaround is to use the MIKE Zero Extraction tool 'Profileseries from 3D file' (you need to define the start-end profile points coordinates (for one ore more profiles) and an appropriate spacing, probably similar to your model domain cell size to make sure you get all the detail along the profile).
2. You can use the MIKE Zero Extraction tool '2D Grid from 3D file'. One of the dialogs of this tool allows to specify a desired slice/plane (XZ, YZ or ZY) from the 3D dfs3 file. The output of this would be a time varying dfs2 grid file which could then be loaded in Result Viewer or Plot Composer to create a video (using the 'Video Forward' button at the "Result Viewer Tools" toolbar).
3. Postprocessing can normally be done using the Grid Editor tools: if you open the dfs2/dfs3 files, the Grid Editor has various postprocessing tools (e.g. select cells by polygon, set/add/subtract/multiply/divide cell values by a user-defined value, apply expression/equation calculations using multiple functions, calculate statistics, copy/add/multiply different grid dfs2 files, ..).
For visualization we would normally use Result Viewer (e.g. for creating videos of a certain output parameter) or Plot Composer (e.g. for creating videos of scenarios comparison or simultaneous animation of different types of outputs).
If you still want to modify/visualize the dfs2/dfs3 files outside MIKE, since these are binary files, you would need to convert them to other formats. E.g. you could use the 'GIS' tools in the MIKE Zero toolbox or some conversion tools in the MIKE Tools webpage (e.g. MIKE2Shape): https://www.mikepoweredbydhi.com/download/mike-by-dhi-tools.
Hope this helps.