re: Is it possible to show a dropdown-list of the citys, my experts (thats what I used your plugin for, an expert overview) are living in?
To filter the directory by? Yes, it is possible. It is a custom solution I sell which includes installation and configuration. You can see an example of it on this site (Find A Therapist section):
That site is not using the city drop down feature but it is available. The top 3 drop downs on this site are three different parent categories. The options are the respective parent children categories (hope that make sense). I know that is not what you are asking for, but I wanted to describe what you were going to see.
If you are interested, let me know and I can provide a quote.
re: Further I want to show the adress at the search results. Is that possible?
Maybe, can you provide a mockup of what you’re asking?