Indeed it looks like a lottery. It's incredible, though, how much it helps to know that someone else shares your unlucky fate.
I actually revised my preliminary questions and they sounded perfect, again this opinion may change if they got timed.
I did the "mistake" of making a pdf cover letter and just paste it in the form when I realised it was supposed to be written there. I don't know why but it sounded just lame written there. On top of that, I really had nothing to answer to "what have you done so far etc. etc.". The only thing I could afford doing was reading books, included pretty hard ones, but I feared it could sound both pretentious and silly to write that. So I wrote nothing, and that was probably even worse.
Well, this summer I promised myself I'll try and get a PPL. In the worst case I'll have something to write on my next cover letter if there will be one.
Thanks to all of you on this forum!