From the log it found the Kindle Previewer 3.50.0 in your wine installation. That seems to be correct. But there may be a problem with the wine command itself. What command line did you use to install the Kindle Previewer?
Could you also run the command below from a terminal. It is similar to the command that the plugin tries to execute. But replace both occurrences of "USERNAME" with your username before. It assumes that you installed Kindle Previewer at the default location that was suggested by the installer. It should output a short documentation of the Kindle Previewer command line.
Code:
wine '/home/USERNAME/.wine/dosdevices/c://users//USERNAME//Local Settings//Application Data//Amazon//Kindle Previewer 3/Kindle Previewer 3.exe' '-help'