In our last house the powder room had about the same sqare feet as yours does, just different dimensions. We had three halogen lights above the mirror and that was plenty of light for everyday use. I don't remember the actual bulb we used as we haven't lived there for almost a year. Just look for sconces that allow a brighter bulb or that use two bulbs in each sconce. I would use the lumen formula davidtay posted above. That will help you decide if the sconces you like will be bright enough. We did have a bathroom fan with a light installed above the toilet. That helped for when I wanted to clean the bathroom, or needed a brighter light for removing slivers, etc. as the bathroom was where we kept our first aid kit, but we could have gotten along fine without it as the light from the vanity fixture was enough for the room.

The reason I don't LARGE face-on photos of family over the fireplace is it just seems like I am being stared at, lol! On the flip side, I covered my mantle at my old house with SMALL photos in ornate frames of friends and family members. Then a large picture/wood block print I loved in the center. I had wall mounted lights that looked like candle sconces on either side of my art, something you might consider., (either the lights or the sconce, well out of the way of little kid hands). That corner curio cabinet is GORGEOUS and I would put something on the mantel with a brown wood tone to tie in with the cabinet. Maybe a picture with a brown frame or some art with some color in it including brown. Or consider adding some colorful art or something on the wall kitty corner from the fireplace, so the room look a little more balanced. I don't see anything wrong with the sailboat photo, but then we are sailing people and love boats and the water and have spent considerable time thus engaged. If you're land-locked and have no association with boats, then it is a little contrived but will do until you find something that speaks to you. If it were me, and I had traveled the world, I would want pictures of that somehow. I have a large travel advertisement picture of a famous place I visited (Valley of the Ten Peaks in Canada, which is often used in Canadian tourism advertisements) which hung over my couch in the living room of my last house, and was surrounded by some other art pieces evoking the northern Rockies. Which made the space feel welcoming to me. Not saying you should copy me, but just sort of showing how you can develop a theme of stuff that reflects your live and loves in your "living" room.

As I have remodelled our bathrooms I have added more lights to them. I like to be able to light up a bathroom all the way from very dim to very bright. I have used a combination of sconces, recessed lights and decorative pendants/chandeliers, all on dimmers. Need to find a spider or clean ... everything on at full power. Taking a relaxing shower late at night ... just the recessed lights in the shower, dimmed all the way down. I like having options and flexibility in my spaces.

I think you'll want to buy two mirrors and three sconces. The balance will work out much better being able to have one above each sink. Furthermore, I would propose getting three lights as that will probably help with ensuring you have more evenly spread lighting to work with in the mirrors. I realize this bathroom vanity is longer but it does have the two mirrors and three lights. Definitely our preference when building.