Is it unusual to send questions that you may have after interview to the interviewer via email?
No, not at all -- it's common for candidates to think of questions they forgot to ask during the actual interview, and to follow up via phone or email.
Would it look good on my part if I reach out to the interviewer via the email and ask him the questions that I have?
Yes. Having questions demonstrates your specific interest in the position and employer. Asking them later via email is fine.
Also, how can I avoid these kind of situations in the future?
From your description, it sounds like the interview was ended abruptly, so I'm not sure this situation could have been avoided, or that you should have done anything differently.
Perhaps you could have asked if they had a time limit on the interview. If they let you know that up front, you may have been able to manage the time a little better, and get your questions in before the interview was over.
But most of the time, as you point out, the interviewer tries to leave sufficient time for questions. When I am interviewing candidates, and I'm running short on time, I cut my own questions short, to make sure I address any outstanding questions the candidate might have.