Asking for a tour of the unit appears intrusive. Asking about the next steps or what your chances are of getting the job is too aggressive. Writing a follow-up letter to the interview is redundant and a waste of the interviewer's time as well as yours. If you decide to take another position before you hear the results of the interview, it's better to withdraw your application without saying why. If you do not get the job, it is not a good idea to discuss the reasons why with the interviewer.
Preparation is essential for successful interviewing.
It also helps you to lower your anxiety and manage your stress. A whopping 90 to 95 percent of communication is nonverbal and takes the form of body language, manner of dress, tone of voice, attitude, and behaviors such as punctuality, assertiveness, etcetera. No one maintains eye contact 100 percent of the time. A better option is to jot down notes about questions you have and wait for the best opportunity to ask them, perhaps at the end of the interview, or when asked if you have questions. However, flexibility is the key here.