Three general questions in silanization of a glass surface
Is this method correct or I should necessarily deep coat the glass plate into a container of silan solution (because in the 2nd method, there are larger number of available agents than can react with glass or have better accessibility to the glass surface)?


Your method is fine, anything method that covers the surface with solution will work.


  How durable is the silanized glass? i.e. after silanization, when I want to clean the glass surface from reaction products, can I rub something onto the surface to help clean it better or the treated layer of glass might be damaged? (rubbing with cleanex, etc)


In my experience hydrophobic coatings are durable, but will wear due the the small surface thickness.  My recommendation is to use rinsing only, if you can and use abrasive cleaning when you have to.


  For getting maximum hydrophobicity, can I use Octadecyltrichlorosilane>90% directly on glass surface (for how much time?) or I should dilute it?


I find that hydrophobic solutions typically make  very effective coatings nearly instantaneously.  You can use it directly which should only require a few seconds maybe a whole minute to work.  If you want to conserve octadecyltrichlorosilane you can dilute it. I have had 5% solutions also work nearly instantaneously, but if you want the most hydrophobic surface you should wait 1-5 minutes.