@tpartner:
Thank you tpartner for your solution!
As far as I checked it, it is working.

And please appoligize, I did not know, that it is necessary to provide only the relevant questions as jelo said "You can just create a small survey and attach the export here. You don't need to provide the complete survey." so I thought it is up to me and of course, I've chose the easiest way. But I will keep that in mind!
But what do you mean by "Minor - when generating a random number, you should always put in a check to see if the number has been previously generated". I thought actually when having 1000 participants, that (almost, because it is random) every 50st will start with no. 1 again. Is that a wrong assumption?
@jelo:
There are several reasons!
First, the panel provider I will be using, uses LimeSurvey too. Therefore, it will be very easy by simply providing them the final file. Second, I can use the Sawtooth company account of a good friend to analyze the data. But I cannot carry out my survey on that, because it is her company account. I checked a lot of different providers besides Sawtooth, however, they are all really expensive - above 1,000 euros per licence. That is why I have chosen LimeSurvey: It provides a lot of possibilites and a proper support.
Yours,
Chrissl