How should I respond to a professor's email following up on an offer of admission?
Well, the potential supervisor explicitly mentions "Please let me know if you have any questions about living and studying here in xxx"...just email him/her if you have any such questions. If you are waiting for offers/rejections, I think a polite reply stating the same would be alright. 

If you are excited to work with him/her because of reasons X,Y,Z, just mention them in the email. In any case, it is highly likely that the potential supervisor understands your position (of waiting for all offers).