I needed the current week number, too. So I have added a template that adds a nice calendar week tag at the top of each note created from this template: \date(format: '#KW'ww)
What’s extra nice is, that I can click on e.g. #KW18 and start a search to see all the notes, that I have created in week number 18.
KW is a common abbreviation for Kalenderwoche (week number) in German. 