I am gona to test it - how long do you expect for this A-F grading? (can I just "rename" it in translation from numbers to letters?)
In this case no, it's really hardcoded as 1-6, if you are in a hurry i am going to bring it with the next bugfix release version.
Is it somehow possible to "skip" step after click to "book" button?
Hmm which step do you mean? You can set the booking form to one page (with the setting) if it is not paid. If it's paid you could disable all payment plugins.
And hopefully last question: If teache is creating event - he need to select "organizer" - but there are listed all joomla users (in my systems more then 1,5k) - is it possible to preconfigure it as there will be automatically creators name, or at least just a "joomla group" with a teachers?
Currently not, have a setting for that (e.g. group select) on my todo-list for one of the next versions.
Kind regards,
Yves