The instructions call for 6" to 'a flammable surface'. The 6" distance has a notation that says "to flammable surface or bottom of hood". I think if you tile it or make it otherwise non-flammable you'll be fine.

The six inch clearance allows for instances where you have large cooking vessels overhanging the side of the range. The heat and flames can duct from underneath the pan up around the sides. The bowls and grates are about 11.25 inches wide on the Bluestar but you may have a skillet/stock pot/wok wider than that. I have a 16" wok, for instance, and it would probably be touching the wall in your configuration.

We don't have marble in our kitchen so I cannot speak about how it performs one way or the other, other than I know it is not considered "flammable" ordinarily. But I would not want flames coming up around the sides of a large pan being ducted right into it, either. Concerns would be discoloration or cracking? Perhaps someone with more experience with marble in the kitchen can chime in with more information on that.

You can always mount a sheet of stainless in that area, rather like a backsplash, to protect the wall. If it were me, I'd probably plan on using the other side of the range for the big pots and pans.

The wall is to the right side of the range. I don't stir fry at the moment, but might start. I think the advice to do this on the left side makes sense. 12" is the widest pan we have right now.