There is a post just below your post from Tyler in which I provided some help for him with his staircase question. Granted, your question is not exactly the same but my Follow-up is close to the same for you.
I will say that this is a job not for the faint of heart. If you're using oak or something, and you make the 'wrong cut', it may be very expensive to 'fix'. As with Tyler, spend some of the money you're saving (by doing it yourself), and get a good book that answers your question(s). It is a very broad question that involves kneewall or no kneewall, safety code(s), half-open or full-open, etc., etc.. I don't think anyone could fully tell you what needs to be done without seeing exactly what you have for that opening. Perhaps there are other neighbors in your neighborhood that have a railing in the location you're interested in finishing. It would be useful to befriend them.
Other than that, perhaps someone else can help you. My best to ya and hope this helps.