OK to ask a professor at my institution with whom I have no previous relationship some questions relating to hobby-project?

One of the perks of being a college or university student is access to the faculty for academic purposes. Ph.D's become professors at community college particularly because they want to be engaged with students and their curiosity without the enormous overhead of excessive grant writing, etc. In short, they basically live to work with curious students like you.

Ok to ask random professor questions relating to hobby-project?

Yes, and if you show half the courtesy and respect in your introduction to the professor that you did in this posting, you can rest assured that the response will be solely a function of his/her current availability.

Yes, it is entirely appropriate, especially if you come to them in person and just knock on their office door when they're around and ask if they can spare 5 minutes to answer a question or two. If you are nice, polite, curious and fun to talk to (and you sound like all of those things to me) they may easily end up talking to you for an hour. Busy or not, professors are people and love to procrastinate just like anyone else. :-)

Email is a lot less likely to work, but again, I don't see it as inappropriate, simply less effective.

And don't overthink it. Knocking on someone's (even a stranger's) office door is not the same as hugging them, and not every decision in life should be agonized over and analyzed in minute detail. Just try it, the worst that can happen is... nothing.

If you don't ask, the odds of getting help are zero.

Admittedly, even if you do ask, you're unlikely to get very far—as you mentioned, the professor doesn't know who you are, and therefore would be very unlikely to respond unless the email is written in such a way as to grab her interest.

However, if you're a student attending the same institution as this professor, asking to set up a meeting might be a more productive route, so long as you show genuine interest in the professor's work. Most professors will take the time to talk to someone who's interested in their work (we're human, and we usually like the attention!).