Thanks decoenthuasiaste! I think we will follow your advice and position the desk that way. This way I'll have the window to my left and can look into the backyard if I want, and also face the large wall where we can place a nice long & short bookcase with art. I think the reading area to my right (on wall that current has guitar and standing lamp) will look great. We are going to try a rug like this one to complement the more modern bamboo desk top and dark navy walls:

There is one set of file drawers on the right side, which you can see in the photo, and in the top drawing. The desk top will go on top of the file drawers and extend around to the left as shown in the yellow shading in the bottom schematic. The supports are not steel. They are wood ledges along the walls, wood support 1.5" deep and 22" wide along the pocket door wall, and then a 3/4" by 8" support perpendicular to the black column. I would love guidance on how the supporting structure needs to be built to safely hold up the desk top.

it will be more of a full-time office, but he travels a lot & visits clients frequently working out of their office What I like about Beverly's last suggestion with the worktop extended along the wall is that also gives your husband more storage for things like files, etc. Without something like that, will he have enough storage in the room? Otherwise I would strongly consider a credenza for storing files, under the TV, rather than a media console. For curtains, given your color preferences, these would be nice, https://www.potterybarn.com/products/haylie-print-drape/?pkey=ccurtains-drapes&isx=0.0.6515 I would also re-hang the curtain rods above the casing and extend them several inches beyond the casing for "stack back". If you opt to buy a rug from PB, exercise caution because historically they've had problems with rugs that smell (generally a "burned latex" odor). Make sure you get a *woven* rug, rather than a tufted rug, esp tufted rugs from India. There's a long thread here somewhere, and also this, https://rugchick.com/pottery-barn-rugs-to-run-from/

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