Main argumentation in introductory chapter of Phd thesis? I am in my last year of my PhD and start focusing on writing my thesis. In the course of my PhD I had to apply twice for external funding, in which I - thanks God - succeeded.

I believe that part of that success was - aside of the "hot" topic - the way I presented my research. I wrote roughly 10 pages in style of a paper, where I had an abstract (5-6 phrases about my research answering the 5 common w-questions) for those who had just 1 minute to spare. However, instead of presenting my text of 8 pages right away, I added first a text of about 1,5 pages in which I wrote about my research in categories like motivation, research gap, my approach and contribution, research questions, method, time and work schedule in greater detail for those who had about 4 minutes to spare.

Is it good practice, a good idea to do the same for my PhD thesis, presenting the major argumentative path in the first chapter "Introduction" on perhaps max. 5 pages? My idea is that the reader (supervisors) do not need to read the entire dissertation to understand/identify the major arguments (but obviously need to, for him/her to challenge my entire work) and to not get tempted to only read the conclusions of each chapter to prevent that they get a sided idea (just in case).

My idea is basically to allow the reader to follow my entire argumentation easier, not to help them skip pages or save them time (like in the case of the funding application).
Every dissertation or thesis should have an introduction. 

When I receive a student's thesis to read, I usually do not have numerous hours to pick out the details of every page. Having a 4-8 page introduction is extremely helpful in allowing me to learn what is most important in the overall arguments of the thesis. An introduction allows readers to see the major theme of the work.

When I wrote my own dissertation, I treated the introduction chapter much like an extended abstract. It highlighted what the reader needed to watch for and established the overall theme of my work. 

The introduction can also serve a useful purpose of providing a place to take care of some of the administrative aspects of the thesis such as acknowledgements and holistic citations ("This thesis was written using LaTeX; all code was written in C++). These things are given their own pages at times, but I found it useful to be able to just place them in a paragraph in the introduction.