Pottery Barn Trenton Shelf: You could use two of these 24" shelves side by side below a large mirror in the entry. Or, I like the style of them, maybe for another part of the house.
Amazon Nathan James Black wall mount or Nutmeg/Black walnut floor - 12" deep. Either of these would be narrow enough for your entry and then we could figure out a mirror to go with them depending on how you want to place them.
Or, you could buy silver or black metal brackets and stain a piece of white oak to match your floor and mount a large mirror above the shelf. Sorry for the sketchy drawing!
I love this huge mirror from Uttermost - good quality. An investment piece but your space needs something BIG.
Hall & Stairwell
Art: Checkout this website for big floating frame canvas prints. Great Big Canvas I like their close-up nature photos that come very large. You could frame in black or silver to go with the other colors in your house. I like the idea of doing a series of 3 of something down the hallway, maybe black and white like this Pin of yours:
A framed floating canvas could work in the stairwell. Some of them come very large, like this which you could hang vertically on one of your two stair walls.
Console tables: check the height on whatever you get before buying to make sure it's not taller than the top of your sectional
All Modern Olson: This one's pretty with the glass shelves, but more fragile. I like the two shelves to cover the back of the sectional.
Trent Austin Console table from Wayfair I like the leg detail on this one.