Don't dwell too much about being specifically "welcoming" to interested amateurs, per se. Our mantra is always "be nice." But make no mistake about it: Build a site for experts with great expert answers, and the less-expert users will take care of themselves.
This is right out of the blog post: Asking the First Questions:
Everyone is welcome. But, in these earliest days, we are DESIGNING a site for experts. To attract experts, you need a site where people are asking very interesting and challenging questions, not the basic questions found on every other Q&A site. Remember, the pro sites WILL attract the enthusiasts, but not the other way around!
The earliest questions on a site will set the tone and topic of the site for a long time.