Someone will have issue with their machine, bad tension, breaking threads, etc. and it will happen to the one person who expects you to do something about it. LOL The last quilting workshop I went to the instructor had a machine set up ready to go for just that reason and yep we had a time hog student who couldn't get her machine to cooperate. How are you going to address the student who is constantly calling you over to 'see why this isn't working"? I think you'll do great as the most important part of teaching is wanting to.