Would you recommend any wall art or mirror?

I would put a table on the leftmost of the walls under the stairs, with a mirror or art over it, and then a bench or pair of ottomans along the wall to the right, in case somebody wants to sit and take off or put on boots, etc.

Alternatively, you could put a round table in the elbow of the space, with a lamp or some tall flowers -- I guess that's why the outlet there.