3.5" which is just fine. 4" is standard and I read that this newly augmented standard is a function of needing space to allow for new, thicker workboots. Dunno if that's true, but there aren't any workboots in my household and quite frankly, even if there were, the 3.5" would accommodate them anyway. I don't know why they're made so big, just cuts down on cabinet space, seems to me. Do a google search on this topic, there have been many discussions of it.

A five foot tall headboard is pretty high. I would wait until it's in the room and then take a photo for us. Generally speaking, a picture or series of pictures going horizontally works well above a bed.

We have the 48" DCS range with griddle. (All gas with two ovens, not the range top). DH had it installed at his old house, and when we sold that house we took the range with us for our new kitchen reno. He has the matching DCS island hood for the range. My husband loves his range. However, he found that occasionally the igniter would keep running even though a burner was lit, which would go away if he turned the thing off and on again. (Personally, I would have had this repaired under warranty, but my husband didn't bother). I don't have any photos of the installation of the range in the new kitchen (but hopefully in three weeks!). I can dig up pictures of the range in my husbands old kitchen if you like, but I'm not sure how useful it would be, as my husband had possibly the oldest and crappiest kitchen in the world (bright orange melamine!) with this powerhouse of a range in the middle of it.

I would be inclined to not put anything there. Maybe try a console table but would have thin as to not hit it as you walk around it. You also have the heat or cold air register near the floor to contend with. Guess you could put one of your dining room chairs there but I still like it just the way it is.