Cool space. I would consider painting the doors a dark charcoal or black (I don’t know about shiny black through, might be too much) but I would not paint the trim. Keep it white. As for the walls, you could do a color, like a light gray blue or green.

I think your idea is good for this home gym, add some body builder poster on wall.

From a countertop fabricator/installer's point of view. If you add new countertops to the existing cabinets, no problem there. The potential issues arise if and when you decide to get all new cabinets and want to use the new countertops. You'll have to get the same fabricator to remove the tops from your original cabinets and then re-install them unto the new cabinets. Other fabricators will not want to take this on as it is fraught with issues. We get asked all the time to do this and we always politely decline. Material breaks, sizing can be off on the new cabinets compared to the original. You would have to keep the cabinet footprint exactly the same and hope it all re-installs perfectly. More often than not homeowners who have done this wind up buying all new countertops, thus doubling your cost for this one portion of your project. Best of luck with your project.

Unfortunately the office in the bedroom is for my husband as he is currently working from home indefinitely and needs the privacy for phone calls and Zoom/Skype meetings. I was planning to have my desk somewhere in the main part of the house as I work at home occasionally, I still go in the office. Our house is 3 Bedrooms, Kitchen, small Casual Family Room in front of kitchen, and large open room (formal dining/living room) in the front entrance that is open concept. unfortunately there are no nooks, basement, or attics in the house which is why our space is limited. Each of the 3 bedrooms has a purpose: Master Bedroom that has limited space, Husbands office and he needs the privacy for phone calls, and the current guest room which will be utilized as a nursery/kids room in near future. The garage has both our cars already and we live in the desert where it gets over 100 degrees. So a gym in the garage is not an option.