Some context would help. What is the purpose of the space?

I would avoid the accent wall. First, they usually are just odd, as a general rule, but especially in this case—you’d only be highlighting the back of a cave-like space with odd boxes jutting into it already (you’d only be making yet one more visual box). I’d focus on minimizing the rectangular boxy-ness of it all, for instance, by getting some cabinetry under and around it where I could. It’s hard to be more specific without more photos from other angles and understanding how/whether you need access to whatever is in there.

You are most likely looking forward to having a creative space. I feel you should make it your own and add colours you love, but not with a feature wall because of the box that’s there. I think you could make it blend in more by adding shelves above it, and adding decorative colourful containers. You could paint your cabinet to coordinate, and I also suggest painting the chair and table legs.

The stereo is huge, can it roll under the table to give you more room? The shelves in the pic above look great. Extend the shelf over the register in the alcove area to visually tie it in and then add more shelves spaced above that for your supplies that wrap into your alcove. Leave some space for a few books and decor mixed in with your supplies in colorful baskets or storage containers. I think it would brighten up the space if you paint the back wall an accent color. Then use all white shelves and your decor/supply containers to break it up. You have the makings of a fun creative space. I would put your mirror on the right wall and maybe give the frame a splash of color as well. Good Luck.