My potential advisor is suggesting a project that I don't think I have the knowledge to take on?
First thing, in a master or in a PhD, you are a student and it's normal to learn new things. If your potential advisor wanted someone for this project that already knew how to do it, he/she would hire a postdoc. Actually, learning new techniques, in statistic or other, is what every scientist do, during their entire career.

Second, you are already planning on taking additional statistical courses and your potential advisor knows your background. It seems to me that you will be fine and that you can do this. This sounds a lot like impostor syndrom and you should read on that. In that case, I wouldn't talk about that to a potential advisor. Do talk about it if you need to, but preferably to professional help or people who know you. For the record, I wouldn't hesitate in talking about impostor syndrom with my advisor, but I know him, he knows me and we have an healthy mentor-mentee relationship...

If you still want to touch the subject with your potentiel advisor, do it simply:


  I'm very interested in this project, but I'm worried I don't currently have to knowledge to do it. Are those courses sufficent to help me with the project? Will there be additional help available ?


This is the good moment to enquire about lab resource, which can be professional statistical help or colleagues. Good luck.