OK to ask a professor at my institution with whom I have no previous relationship some questions relating to hobby-project? I go to community college so our professors aren't busy with lab research. They're still busy people though and I wish to respect that.

I'm pretty much just working through some neuroscience textbooks for the sheer heck of it, but I often get stuck. It would take forever to ask every single question on the internet. Plus, sometimes a discussion with a real person is just better in many ways; it could lead to further questions and answers plus instant clarifications. 

Thus, would it be weird/wrong to just ask a random professor (with whom I've never taken a class...just one with the relevant biology expertise) for help with specific questions about my side project?

I'm guessing it depends on the professor; but on a scale of 1-10 how weird/ intrusive would this be? I mean, some people would be ok with getting hugged by strangers, but that doesn't mean it's a good idea to try and hug them.
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.