What if you turned the desk so the person sitting is facing out rather than looking into the mirror. Look into getting a square rug for the space. what about some floating shelves for storage on the bike wall? What is around that corner? I found two cool options for the mirror wall one would use command strips to mount artwork: https://www.apartmenttherapy.com/plagued-with-dated-mirrored-walls-5-design-ideas-to-make-them-work-241744 or put a film or decal on them: https://www.spancraft.com/antique-mirror-collection.html

It would have to be around the same size as the printer box that is there right now and the door will open no problem. So no larger than a a couple feet wide. Our home is more on the traditional side but we have some modern furniture. I would say transitional is the best description of style! We also need an office chair that will match the chaise.

First of all, I love the wet bar. I have one by my desk and it’s wonderful to have tea, coffee, water nearby. Your guests will also appreciate it - leave a bottle of wine, wine glasses and snacks out for them. A good quality sofa sleeper can sleep guests, provide seating, and will give you more space while you’re using the room as an office. Add side tables and lamps, it will be a nice place to read too. Place your cabinet on the far wall that doesn’t have a window and float your desk in front of it. The sofa can go on the opposite wall, near the entry. Place your keyboard under the window opposite the wet bar and roll your office chair over when you play. If you don’t need the ceiling fan, a beautiful light fixture can be swagged above your desk.

You can make this space so cute. I’d do different material on each wall... but to answer your question- I’d put hard hats. Maybe some cool antique looking truck ...