Type of Post Interview Follow Up Questions? How many is too much? Interviewer repeated three times during interview and in reply to thank you email, "please ask any additional questions"

As stated, my interview went okay, but he repeatedly asked to let him know if I had any questions. 3 times during interview and also in his reply to my thank you note. 

I do have questions, but do not know if I should get detailed, and also ask more than 1 or 2.