I just passed my kontolfahrt a week ago. So I don't repeat myself, you can read up more about my experience on the link below: [Drivers licence] Conversion and questions
I was extremely nervous about it also but it all went well. After doing your eye test, filling in the form and sending it out, and receiving an invite for the test from the authorities, I would suggest that you take a try out lesson with an instructor. Only then can the instructor tell you approximately how many lessons it'll take you to drive properly in CH.
My wife took over 23 lessons where as I took only 5. However, I've been driving for many years and am an avid motorsports fan and ex-competitor. There are instructors out there who speak English and I can give you the details for the one I used. She's fair, pleasant, a very good instructor and speaks English.
Also for the kontrolfahrt, the examiners do speak a little bit of English. However, I'd learn the simple directions such as left, right, straight on, junction, highway etc... in German. Also please note, kontolfahrts can be done in a number of locations. If you're nervous about trams, too many pedestrians and traffic, I'd suggest you don't do it in Zürich city centre. Do it in Hinwil ,where I did.
Send in the paperwork, then get an instructor. I'm sure you'll do fine.
Wish u the best.