I have a brown leather sofa in a room with gray walls and white trim and I love it. I have warm (mahogany and cherry) wood furniture as well. I think the contrast of warm and cool is great, just be sure to repeat it somewhere so it's not just one single element that stands out. I think wood floors will go a long way (preferably with a rug under the sectional).

I agree that the style of the brown recliner is off for the couch and the room, but to your questions, yes, grays and browns can work nicely together. Just look at a forest in the winter. Understand that I have been using gray for over 30 years well before it was trendy-- since way back in 1987 when I painted my kitchen cabinets and the trim work in the kitchen, breakfast room and adjoining den a greige called "Norwegian Wood." In my new house, I am using gray couches (smililar to the one you show) with brown leather chairs (in fact two different browns, one a grayer brown and the other a bit redder Brown, inspired from my fireplace stone that has grays, browns, rusts and camel (or a caramelly yellow color). I did bring in more colors and warmth from the rusts and caramels in the stone with a rug, but also a bit of blue with the rug, blinds, pillows and other elements. I am not a pro and others tastes may differ, but the look pleases me and I find it serene.

Lovely space and a lot of great choices already. If you’re willing to switch out the dark brown dresser, would you consider painting it? Maybe a pale blue chalk paint if you’re bring in a few blue/teal/green accents? On the other hand, if you lighten up some of the pieces in your vignette, keeping it the way it is could still work. Find a selection of clear green and turquoise bottles to replace the black ones in your vignette. The lamp is a little too far to the right, the tray with bottles needs to move a smidge to the left. Try covering the books in white to repeat the white from other pieces in the room. I’m an allergy sufferer myself, so I completely get the no rug thing. And all throws and pillow covers must be washable, etc. Regarding plants and dust... very easy solution for that is to give your plants a shower every so often. This works incredibly well to keep them watered, dust and insect free, and is really easy to do. I use cool water (not completely cold) and don‘t turn the water on full blast so that it’s fairly gentle on the plants. Leave it in there for a bit to drain, and then they can go back to their normal spot.

Brown leather can look classic but the ubiquitous puffy brown recliner/sectional furniture in stores can easily dominate a room and grab all the light out of it. You can balance a room with a brown sofa with accent color pillows, good lighting and a new rug. Finding a sofa with a size and style that fits your room and has a pleasing shape will make a big difference as well.