The automatic export of bokeh-plots does not work, why?

You’re likely seeing a warning refering to missing installs of selenium and/or phantomjs-prebuilt. While selenium should be included in the requirements, phantomjs-prebuilt is not a pip-install. Please refer to the documentation of phantomjs or bokeh to see how installation works (usually npm install -g phantomjs-prebuilt should do the trick).

What is the ta_exec_dir-option good for?

The ta_exec_dir specifies the target algorithm execution directory. With this option you can run CAVE from any folder, just make sure the relative paths in the scenario can be found from the path you specify in ta_exec_dir. This option is currently needed for SMAC-file format (and CSV, depending on the data).