Aim at least 24" between the hood and range. Backsplash usually don't go below the countertop.

Is 30" adequate? I have read a few comments about it being too low. I am only 5'3" so 30" seems good for me, but sometimes other people cook at my house. Also, when I bought the hood and tried to buy a backsplash, the Viking rep said that the 36" x 30" hood wasn't going to work unless I had the 8" riser on the range (I don't). The gas pipe piece extends out of a hole in the back of the range. The top of the hole is exactly 5" below the top of the range. I want to have the fabricator make the backsplash 36" x 34-1/2" if I am going to set the hood 30" above the range. I have the luxury of making this decision, because the whole wall has to be reframed, as the range sits 5" from the wall due to the gas pipe that sticks out of the back, and there is currently no hood.
I appreciate your responding and would like your thoughts on this matter. The fabricator that I found will make this backsplash for less than I can buy the 36" x 30" backsplash from Viking.

The specifications/installation instructions for the range generally will indicate what the manufacturer thinks is the best distance from the range to the bottom of the range hood. 24" would generally be considered too low over a gas range. We generally shoot for 30", but defer to the manufacturer for guidance.

Thanks for everyone's help. The range book says 30-36". I went ahead and ordered a 36" x 34-1/2" backsplash, hemmed on the left and right. I'll hope for the best.