Do professors like answering questions from non-students/private citizens?

As in general, people are typically happy to be asked to exercise/express their expertise on the things they've worked their whole lives to understand.

But/and the most expert people are very busy, working on moving forward in that.

So their time is very valuable.

So an email response is much preferred, typically. The email back-and-forth, to arrange a physical meeting, is not preferred...

And if I, for one, found out that my opinion as a professional whatever was just supposed to be one vote out of some larger number... for the potentially misguided project of an amateur... I'd most likely not agree to spend the time. It's disrespectful, whatever you feel about that, for non-experts to think that the time of experts is at their disposal in this way, for free, etc. Be serious.

Many academics are kind and generous, but like to have just a token of respect and appreciation (rather than big bucks).

Most researchers I know - including myself - are happy to discuss honest questions from the public. What most researchers do not particularly like, is to be part of a session where the asker either has a hidden agenda (why don't you just ask your question in an email?) or does not put any value to the time put into doing such sessions (do you really need to ask multiple professors? To me, that approach would put you directly in the spam category).

I would suggest that you simply write the question directly to the professor suggesting you to meet up with the grad student, and possibly ask him/her to forward it.

STOP. If you have an agenda (such as asking and comparing answers) this will be rapidly known, especially if you limit yourself to a single university.

Please read a lot of relevant literature before contacting anyone: if you are not current with the literature chances are your meetings will be very short and you will be ignored as yet another crackpot amateur. Bear in mind that your chances of successfully publishing as a non-student/private citizen are extremely small.

Note: Unfortunately every so often I meet someone with an alternate method to solve a question for which the current paradigm works perfectly well. There’s no harm in this of course, but the method fails at any other problem except the original. In all cases I can remember the author had not done proper prior research and did not realize how much the current paradigm explained, and how little this new approach did beyond the initial problem. Often non-specialist fail to appreciate the level of professionalism required to perform at the research level in any field.

As a result, most non-specialists are dismissed simply because of poor background preparation. All crackpots fall in this category but not all in this category are crackpots so it is incumbent on the non-specialist to be well prepared.