I wouldn't add any furniture below given the limited space. :)

Not sure you require anything but if you need to store something perhaps a wall mounted floating cabinet.

I think it looks fine as is. If you need more storage, I like the idea of basket with blankets.

You've done a wonderful job on: a) choosing beautiful artwork for your wall. b) the placement of the artwork. I don't think you need anything under your artwork, however, if you have a prop - like the coffee table, then move it over to the wall to see if it helps you decide.

like Dan D said above, 2 poufs would work great to fill that void and provide additional seating or serve as ottomans/footstools, if needed

something solid with a hinged lid with the back cut out and the router and stuff inside it. you can put a vent at the left end if you need even more ventilation.