Let's be careful about setting up a bunch of rules before you have an actual problem. Otherwise we are only setting this site up to be one big rule book making this place very user-unfriendly, even for engineers.
Don't worry about this nebulous idea of "hobbyist questions." Wait until you are actually inundated with questions about how to build a lightsaber. Or folks are endlessly asking when we're going to have personal robot butlers. Then maybe (just maybe) you'll have something to discuss; namely, specific classes of questions that might be problematic IN ACTUAL PRACTICE.
Historically, we've had this notion that, if we can just keep out the beginners, the hobbyists, and the folks asking "homework questions", it will clear the way for the "real experts" to show up. Unfortunately, that rarely works in actual practice. Certainly you have to control your scope, but not by dictating what level of interest a user engages in this subject.
Certainly you should assure users are providing enough information to receive a professional/expert answer… but as a rule of thumb, you should determine your scope by discussing specific questions you feel are problematic and then — this is really important — OVER TIME identifying common factors shared by them and not shared by questions generally accepted as reasonable.
Just don't be too quick to start anticipating all the problems you might have… and then start setting up a bunch of rules to ward off those uninitiated hordes.
It's a poor way to start this site.